Urinary calprotectin and the distinction between prerenal and intrinsic acute kidney injury

Summary

Background and objectives

To date there is no reliable marker for the differentiation of prerenal and intrinsic acute kidney injury (AKI). We investigated whether urinary calprotectin, a mediator protein of the innate immune system, may serve as a diagnostic marker in AKI.

Design, setting, participants, & measurements

This was a cross-sectional study with 101 subjects including 86 patients with AKI (34 prerenal, 52 intrinsic including 23 patients with urinary tract infection) and 15 healthy controls. Assessment of urinary calprotectin concentration was by ELISA and immunohistochemistry of kidney biopsy specimens using a calprotectin antibody. Inclusion criteria were: admission to hospital for AKI stage 1 to 3 (Acute Kidney Injury Network); exclusion criteria were: prior renal transplantation and obstructive uropathy.

Results

Median urinary calprotectin was 60.7 times higher in intrinsic AKI (1692 ng/ml) than in prerenal AKI (28 ng/ml, p <0.01). Urinary calprotectin in prerenal disease was not significantly different from healthy controls (45 ng/ml, p = 0.25). Receiver operating curve curve analysis revealed a high accuracy of calprotectin (area under the curve, 0.97) in predicting intrinsic AKI. A cutoff level of 300 ng/ml provided a sensitivity of 92.3% and a specificity of 97.1%. Calculating urinary calprotectin/creatinine ratios did not lead to a further increase of accuracy. Immunostainings of kidney biopsies were positive for calprotectin in intrinsic AKI and negative in prerenal AKI.

Conclusions

Accuracy of urinary calprotectin in the differential diagnosis of AKI is high. Whereas calprotectin levels in prerenal disease are comparable with healthy controls, intrinsic AKI leads to highly increased calprotectin concentrations.     

Urinary Biomarkers and Progression of AKI in Patients with Cirrhosis

Background and objectives

AKI is a common and severe complication in patients with cirrhosis. AKI progression was previously shown to correlate with in-hospital mortality. Therefore, accurately predicting which patients are at highest risk for AKI progression may allow more rapid and targeted treatment. Urinary biomarkers of structural kidney injury associate with AKI progression and mortality in multiple settings of AKI but their prognostic performance in patients with liver cirrhosis is not well known.

Design, setting, participants, & measurements

A multicenter, prospective cohort study was conducted at four tertiary care United States medical centers between 2009 and 2011. The study comprised patients with cirrhosis and AKI defined by the AKI Network criteria evaluating structural (neutrophil gelatinase–associated lipocalin, IL-18, kidney injury molecule-1 [KIM-1], liver-type fatty acid–binding protein [L-FABP], and albuminuria) and functional (fractional excretion of sodium [FENa]) urinary biomarkers as predictors of AKI progression and in-hospital mortality.

Results

Of 188 patients in the study, 44 (23%) experienced AKI progression alone and 39 (21%) suffered both progression and death during their hospitalization. Neutrophil gelatinase–associated lipocalin, IL-18, KIM-1, L-FABP, and albuminuria were significantly higher in patients with AKI progression and death. These biomarkers were independently associated with this outcome after adjusting for key clinical variables including model of end stage liver disease score, IL-18 (relative risk [RR], 4.09; 95% confidence interval [95% CI], 1.56 to 10.70), KIM-1 (RR, 3.13; 95% CI, 1.20 to 8.17), L-FABP (RR, 3.43; 95% CI, 1.54 to 7.64), and albuminuria (RR, 2.07; 95% CI, 1.05–4.10) per log change. No biomarkers were independently associated with progression without mortality. FENa demonstrated no association with worsening of AKI. When added to a robust clinical model, only IL-18 independently improved risk stratification on a net reclassification index.

Conclusions

Multiple structural biomarkers of kidney injury, but not FENa, are independently associated with progression of AKI and mortality in patients with cirrhosis. Injury marker levels were similar between those without progression and those with progression alone.     

Incorporation of Biomarkers with the Renal Angina Index for Prediction of Severe AKI in Critically Ill Children

Background and objectives

Novel AKI biomarkers carry variable performance for prediction of AKI in patients with heterogeneous illness. Until utility is demonstrated in critically ill patients outside of the cardiopulmonary bypass population, AKI biomarkers are unlikely to gain widespread implementation. Operationalization of an AKI risk stratification methodology, termed renal angina, was recently reported to enhance prediction at the time of intensive care unit admission for persistent severe AKI. The renal angina index (RAI) was developed to provide the clinical context to direct AKI biomarker testing. This study tested the hypothesis that incorporation of AKI biomarkers in patients fulfilling renal angina improves the prediction of persistent severe AKI.

Design, setting, participants, & measurements

In a multicenter study of 214 patients admitted to the pediatric intensive care unit with sepsis, the discrimination of plasma neutrophil gelatinase–associated lipocalin (NGAL), matrix metalloproteinase-8 (MMP-8), and neutrophil elastase-2 (Ela-2) were determined individually and in combination with the RAI for severe AKI. Net reclassification improvement (NRI) and integrated discrimination improvement (IDI) were calculated.

Results

Individual biomarkers demonstrated marginal discrimination for severe AKI (area under curve [AUC]: NGAL, 0.72; MMP-8, 0.68; Ela-2, 0.72), inferior to prediction by the clinical model of the RAI (AUC=0.80). Incorporation of each biomarker significantly added to the renal angina model AKI prediction (AUC=0.80, increased to 0.84–0.88; P<0.05 for each). The inclusion of each biomarker with the RAI demonstrated NRI (0.512, 0.428, and 0.545 for NGAL, MMP-8, and Ela-2, respectively; all P<0.03) and IDI (0.075 for Ela-2). The inclusion of both Ela-2 and NGAL with RAI demonstrated an NRI of 0.871 (P<0.001) and an IDI of 0.1 (P=0.01).

Conclusions

This study shows that incorporation of AKI biomarkers into the RAI improves discrimination for severe AKI. The RAI optimizes the utility of AKI biomarkers in a heterogeneous, critically ill patient population.     

Urinary Biomarkers in the Early Detection of Acute Kidney Injury after Cardiac Surgery

Background and objectives: Serum creatinine (Scr) does not allow for early diagnosis of acute kidney injury (AKI). The diagnostic utility of urinary kidney injury molecule-1 (KIM-1), N-acetyl-β-D-glucosaminidase (NAG), and neutrophil gelatinase associated lipocalin (NGAL) was evaluated for the early detection of postoperative AKI in a prospective study of 90 adults undergoing cardiac surgery.Designs, setting, participants, & measurements: Urinary KIM-1, NAG, and NGAL were measured at 5 time points for the first 24 h after operation and normalized to the urinary creatinine concentration after cardiac surgery. Receiver-operating characteristic curves were generated and the areas under the curve (AUCs) compared for performance of biomarkers in detection of postoperative AKI.Results: Thirty-six patients developed AKI, defined as an increase in Scr of ≥0.3 mg/dl within 72 h after surgery. The AUCs for KIM-1 to predict AKI immediately and 3 h after operation were 0.68 and 0.65; 0.61 and 0.63 for NAG; and 0.59 and 0.65 for NGAL, respectively. Combining the three biomarkers enhanced the sensitivity of early detection of postoperative AKI compared with individual biomarkers: the AUCs for the three biomarkers combined were 0.75 and 0.78. The performance of combining biomarkers was even better among 16 early postoperative AKI patients with AUCs of 0.80 and 0.84, respectively.Conclusions: The results of this study support that a combination of urinary biomarkers may allow for early detection of postoperative AKI after cardiac surgery before a rise in Scr.Acute kidney injury (AKI) is an important cause of morbidity and mortality in hospitalized patients (1). The incidence of hospital-acquired AKI varies from 5% in patients with normal preoperative renal function to 25% in intensive care unit (ICU) patients (2–4). Mortality rates of patients with postoperative AKI range from 40 to 60% among ICU patients who require a renal replacement therapy (5–7). Dialysis remains the only U.S. Food and Drug Administration approved treatment option for established AKI.Recently, two new definitions of AKI have been developed: RIFLE (risk, injury, failure, loss, and ESRD) and AKIN (acute kidney injury network) criteria (8,9). It is, however, a challenge to detect AKI in a timely fashion with current RIFLE and AKIN criteria because these definitions are entirely based on increases of serum creatinine (Scr) or decreases of urine output. Scr is insensitive for the early detection of AKI because the change in Scr does not discriminate the time and type of renal insult or the site and extent of glomerular or tubular injury (8,10).Several proteins and biochemical markers emerged as sensitive and specific biomarkers capable of detecting acute tubular injury early and proved to be promising biomarkers as indicators of AKI in recent human studies (11,12). These include N-acetyl-β-D-glucosaminidase (NAG), neutrophil gelatinase associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), cystatin C, and IL-18 (13–25). However, there are no previously reported data for the temporal expression pattern of urinary KIM-1 and NAG before the development of AKI in adult patients. In addition, there is a large discrepancy in the performance of NGAL as an early AKI marker between adult and pediatric AKI patients (15,17,19,20). Furthermore, there are few data on the influence of prolonged duration of storage at −80°C and the number of freeze-thaw cycles on stability of urinary biomarkers at the present time, which will be critical to ongoing validation studies of potential tandem AKI biomarkers (26).In this study, we studied the diagnostic utility of urinary KIM-1, NAG, and NGAL as biomarkers separately and in combination for the early detection of postoperative AKI and the temporal expression patterns of urinary biomarkers before the development of postoperative AKI in patients undergoing cardiac surgery. In addition, the stability of urinary KIM-1, NAG, and NGAL were tested with various handling and storing conditions to evaluate the accuracy of the biomarker measurement because our prospective collected urine samples were frozen at −80°C for 1 yr and were subjected to at least two freeze-thaw cycles before measurement for KIM-1 and NAG.     

Time of injury affects urinary biomarker predictive values for acute kidney injury in critically ill,non-septic patients

Background

The predictive value of acute kidney injury (AKI) urinary biomarkers may depend on the time interval following tubular injury, thereby explaining in part the heterogeneous performance of these markers that has been reported in the literature. We studied the influence of timing on the predictive values of tubular proteins, measured before the rise of serum creatinine (SCr) in critically ill, non-septic patients.

Methods

Seven hundred adult critically ill patients were prospectively included for urine measurements at four time-points prior to the rise in serum creatinine (T?=?0, -16, -20 and -24 h). Patients with sepsis and or AKI at ICU entry were excluded. The urinary excretion of the proteins, neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1), which are up-regulated in the distal and proximal tubules, respectively, were measured as well as the constitutive cytoplasmatic enzymes, π- and α-glutathione-S-transferase (GST), which are released by the distal and proximal tubules, respectively.

Results

Five hundred and forty-three subjects were eligible for further analyses; however, 49 developed AKI in the first 48 h. Both NGAL (P?=?0.001 at T?=?-24 vs. non-AKI patients) and KIM-1 (P?<?0.0001 at T?=?0 vs. non-AKI patients) concentrations gradually increased until AKI diagnosis, whereas π- and α-GST peaked at T?=?-24 before AKI (P?=?0.006 and P?=?0.002, respectively vs. non-AKI patients) and showed a rapid decline afterwards. The predictive values at T?=?-24 prior to AKI were modest for π- and α-GST, whereas NGAL sufficiently predicted AKI at T?=?-24 and its predictive power improved as the time interval to AKI presentation decreased (area under the receiver operating characteristic curve; AUC?=?0.79, P?<?0.0001). KIM-1 was a good discriminator at T?=?0 only (AUC?=?0.73, P?<?0.0001).

Conclusions

NGAL, KIM-1, pi- and alpha-GST displayed unique and mutually incomparable time dependent characteristics during the development of non-sepsis related AKI. Therefore, the time-relationship between the biomarker measurements and the injurious event influences the individual test results.

     

Diagnostic Value of Urine Microscopy for Differential Diagnosis of Acute Kidney Injury in Hospitalized Patients

Background and objectives: Urine microscopy is the oldest and one of the most commonly used tests for differential diagnosis of acute kidney injury (AKI), but its performance has not been adequately studied in the setting of AKI.Design, setting, participants, & measurements: Fresh urine samples were obtained from 267 consecutive patients with AKI, and urinary sediment was examined. The cause of AKI was assessed at two time points: (1) Before urine microscopy diagnosis and (2) after patient discharge or death (final diagnosis). A urinary scoring system also was created on the basis of casts and renal tubular epithelial cells (RTEC) to differentiate acute tubular necrosis (ATN) from prerenal AKI.Results: The urinary sediment scoring system was highly predictive of the final diagnosis of ATN. In patients with a high pretest probability of ATN (initial diagnosis of ATN), any casts or RTEC (score ≥2) resulted in very high positive predictive value and low negative predictive value for a final diagnosis of ATN. In patients with a low pretest probability of ATN (initial diagnosis of prerenal AKI), lack of casts or RTEC on urinary sediment examination had a sensitivity of 0.73 and specificity of 0.75 for a final diagnosis of prerenal AKI. The negative predictive value of lack of casts or RTEC in patients with low pretest probability of disease was 91%.Conclusions: Urine sediment examination is a valuable diagnostic tool for confirming the diagnosis of ATN. A score of ≥2 on an ATN urinary sediment scoring system is an extremely strong predictor of ATN.Urine microscopy is the oldest and one of the most commonly used tests for differential diagnosis of acute kidney injury (AKI). The diagnosis of AKI is currently and primarily based on measurement of serum creatinine, blood urea nitrogen, and urine output. In addition to these parameters, urine biochemistry and microscopy provide the vital information in the differentiation of AKI into traditional categories of prerenal azotemia and acute tubular necrosis (ATN) (1–5). Therapies and prognosis for prerenal AKI and ATN differ substantially; therefore, early clinical differentiation is important. Although urine microscopy with sediment examination is commonly suggested for patients with AKI in the literature, its precise diagnostic value is not clearly known. Furthermore, there has been a gradual trend away from routine urine microscopy in the clinical evaluation of AKI.Urinary microscopy in patients with ATN classically is described as containing renal tubular epithelial cells (RTEC), RTEC casts, granular casts, and muddy brown or mixed cellular casts, whereas sediment in patients with prerenal AKI usually demonstrates occasional hyaline or fine granular casts (6–10). Because urine microscopy is readily available, rapid, and inexpensive, valuable information that will improve the differential diagnosis of AKI might be quickly obtained from this test. The aims of this study were to describe the urinary sediment findings in a cohort of patients with AKI and to determine the performance of urinary sediment examination for differentiation between ATN and prerenal AKI, the most common causes of AKI in the hospital.     

Urinary Biomarkers and Risk of ESRD in the Atherosclerosis Risk in Communities Study

Background and objectives

Liver fatty acid binding protein (L-FABP), kidney injury molecule 1 (KIM-1), N-acetyl-β-d-glucosaminidase (NAG), and neutrophil gelatinase–associated lipocalin (NGAL) are urinary markers of tubular injury that may also be markers of chronic kidney damage. We evaluated the association of these markers with incident ESRD in a community-based sample from the Atherosclerosis Risk in Communities Study.

Design, setting, participants, & measurements

This was a matched case-control study of 135 patients with ESRD and 186 controls who were matched on sex, race, kidney function, and diabetes status at baseline (Atherosclerosis Risk in Communities Study visit 4, 1996–1998). Urinary KIM-1 indexed to creatinine (Cr), NAG/Cr, NGAL/Cr, and L-FABP/Cr were measured in stored spot urine samples from the baseline examination. Associations of KIM-1/Cr, NAG/Cr, and NGAL/Cr with patients with incident ESRD through 2008 were modeled continuously and categorically (quartiles) using conditional logistic regression. L-FABP/Cr was modeled only categorically because of a large number of measurements below the lower limit of detection for the assay (2.4 ng/ml).

Results

No significant associations were observed for NAG/Cr, NGAL/Cr, or L-FABP/Cr with ESRD. Those in the highest category for KIM-1/Cr had a higher risk of ESRD compared with those with undetectable biomarker levels (reference group) in unadjusted models (odds ratio, 2.24; 95% confidence interval, 1.97 to 4.69; P=0.03) or adjustment for age (odds ratio, 2.23; 95% confidence interval, 1.06 to 4.67; P=0.03). This association was attenuated with additional adjustment for baseline kidney function (odds ratio, 2.02; 95% confidence interval, 0.95 to 4.31; P=0.07 after additional adjustment for eGFR and natural log of the urinary albumin-to-creatinine ratio). No association between KIM-1/Cr and ESRD was found when KIM-1/Cr was analyzed as a continuous variable.

Conclusions

Elevated urinary KIM-1/Cr may be associated with a higher risk of incident ESRD, but it does not add to risk prediction after accounting for traditional markers of kidney function in this population.     

Preimplant Histologic Acute Tubular Necrosis and Allograft Outcomes

Background and objectives

The influence of deceased-donor AKI on post-transplant outcomes is poorly understood. The few published studies about deceased-donor preimplant biopsy have reported conflicting results regarding associations between AKI and recipient outcomes.

Design, setting, participants, & measurements

This multicenter study aimed to evaluate associations between deceased-donor biopsy reports of acute tubular necrosis (ATN) and delayed graft function (DGF), and secondarily for death-censored graft failure, first adjusting for the kidney donor risk index and then stratifying by donation after cardiac death (DCD) status.

Results

Between March 2010 and April 2012, 651 kidneys (369 donors, 4 organ procurement organizations) were biopsied and subsequently transplanted, with ATN reported in 110 (17%). There were 262 recipients (40%) who experienced DGF and 38 (6%) who experienced graft failure. DGF occurred in 45% of kidneys with reported ATN compared with 39% without ATN (P=0.31) resulting in a relative risk (RR) of 1.13 (95% confidence interval [95% CI], 0.9 to 1.43) and a kidney donor risk index–adjusted RR of 1.11 (95% CI, 0.88 to 1.41). There was no significant difference in graft failure for kidneys with versus without ATN (8% versus 5%). In stratified analyses, the adjusted RR for DGF with ATN was 0.97 (95% CI, 0.7 to 1.34) for non-DCD kidneys and 1.59 (95% CI, 1.23 to 2.06) for DCD kidneys (P=0.02 for the interaction between ATN and DCD on the development of DGF).

Conclusions

Despite a modest association with DGF for DCD kidneys, this study reveals no significant associations overall between preimplant biopsy-reported ATN and the outcomes of DGF or graft failure. The potential benefit of more rigorous ATN reporting is unclear, but these findings provide little evidence to suggest that current ATN reports are useful for predicting graft outcomes or deciding to accept or reject allograft offers.     

Assessment of KDIGO Definitions in Patients with Histopathologic Evidence of Acute Renal Disease

Background and objectives

AKI is a clinical syndrome with various causes involving glomerular, interstitial, tubular, and vascular compartments of the kidney. Acute kidney disease (AKD) is a new concept that includes both AKI and the conditions associated with subacute decreases in GFR (AKD/non-AKI). This study aimed to investigate the correlation between AKI/AKD defined by clinical presentation and diffuse histologic criteria for acute abnormalities based on renal biopsy.

Design, setting, participants, & measurements

All 303 patients who were histologically diagnosed as having acute tubular necrosis (ATN), acute tubulointerstitial nephritis, cellular crescentic GN, acute thrombotic microangiopathy, or complex lesions on renal biopsy from January 2009 to December 2011 were enrolled in the study. The 2012 Kidney Disease Improving Global Outcomes AKD/AKI definitions were applied to classify patients as follows: AKI, AKD/non-AKI, non-AKD, or unclassified.

Results

A total of 273 patients (90.1%) met the AKD criteria; 198 patients (65.3%) were classified as having AKI according to serum creatinine (SCr) and urine output criteria. The urine output criteria added 4.3% to the SCr criteria and reclassified 6.7% of the AKI cases into higher stages. Of patients with ATN on pathology, 79.2% met AKI criteria; this was a higher percentage than for those who had other individual pathologic lesions (50%–64%). The major cause of not being defined as having AKI was a slower SCr increase than that required by the definition of AKI (98, 93.3%). Patients with AKI had more severe clinical conditions and worse short-term renal outcome than those in the non-AKI group.

Conclusions

Diffuse, acute abnormality defined by renal biopsy and AKI defined by clinical presentation are two different entities. Most patients who have diffuse acute histologic findings met the criteria for AKD, whereas only two thirds met the definition of AKI.     

Kinetic eGFR and Novel AKI Biomarkers to Predict Renal Recovery

Background and objectives

Prompt recognition of severe renal impairment could improve the early management of critically ill patients. We compared the value of kinetic eGFR, plasma neutrophil gelatinase–associated lipocalin (NGAL), and urine tissue inhibitor of metalloproteinase-2 and urine insulin-like growth factor–binding protein 7 ([TIMP-2]*[IGFBP7]) in predicting short-term recovery from AKI and major adverse kidney events.

Design, setting, participants, & measurements

During the 6-month study period, 245 patients were admitted to our intensive care unit. This study included 57 consecutive patients presenting with AKI within the first 24 hours after admission. AKI markers were evaluated at inclusion (day 0) and 24 hours later (day 1). Kinetic eGFR was calculated on day 1 according to serum creatinine evolution. Renal recovery was defined as normalization of serum creatinine with reversal of oliguria within 48 hours. Major adverse kidney events included death, need for RRT, or persistence of renal dysfunction at hospital discharge.

Results

Plasma NGAL and [TIMP-2]*[IGFBP7] predicted renal recovery, with area under the receiver-operating characteristic curve (AUC-ROC) values between 0.70 and 0.79 at inclusion. Although plasma NGAL values frequently reached the maximal measurement range, their decrease on day 1 predicted recovery. The kinetic eGFR calculation after initial resuscitation provided the best AUC-ROC value for renal recovery, at 0.87. The best predictions for major adverse kidney events were provided by [TIMP-2]*[IGFBP7] and kinetic eGFR (equal AUC-ROCs of 0.81). Combining AKI markers in addition to clinical prediction models improved the discrimination and reclassification of patients who will recover from AKI or suffer from major adverse kidney events.

Conclusions

Biomarkers of kidney damage predicted short-term renal recovery and major adverse kidney events for an unselected cohort of critically ill patients. Calculating the kinetic eGFR imposed a delay after initial resuscitation but provided a good diagnostic and prognostic approach. The utility of functional and damage AKI marker combinations in addition to clinical information requires validation in larger prospective studies.     

Acute kidney injury episodes and chronic kidney disease risk in diabetes mellitus

Summary

Background and objectives

Prior studies have examined long-term outcomes of a single acute kidney injury (AKI) event in hospitalized patients. We examined the effects of AKI episodes during multiple hospitalizations on the risk of chronic kidney disease (CKD) in a cohort with diabetes mellitus (DM).

Design, setting, participants, & measurements

A total of 4082 diabetics were followed from January 1999 until December 2008. The primary outcome was reaching stage 4 CKD (GFR of <30 ml/min per 1.73 m²). AKI during hospitalization was defined as >0.3 mg/dl or a 1.5-fold increase in creatinine relative to admission. Cox survival models examined the effect of first AKI episode and up to three episodes as time-dependent covariates, on the risk of stage 4 CKD. Covariates included demographic variables, baseline creatinine, and diagnoses of comorbidities including proteinuria.

Results

Of the 3679 patients who met eligibility criteria (mean age = 61.7 years [SD, 11.2]; mean baseline creatinine = 1.10 mg/dl [SD, 0.3]), 1822 required at least one hospitalization during the time under observation (mean = 61.2 months [SD, 25]). Five hundred thirty of 1822 patients experienced one AKI episode; 157 of 530 experienced ≥2 AKI episodes. In multivariable Cox proportional hazards models, any AKI versus no AKI was a risk factor for stage 4 CKD (hazard ratio [HR], 3.56; 95% confidence interval [CI], 2.76, 4.61); each AKI episode doubled that risk (HR, 2.02; 95% CI, 1.78, 2.30).

Conclusions

AKI episodes are associated with a cumulative risk for developing advanced CKD in diabetes mellitus, independent of other major risk factors of progression.     

Clinical Significance of Urinary Biomarkers in Patients With Primary Focal Segmental Glomerulosclerosis

Background

Focal segmental glomerulosclerosis (FSGS) is often accompanied with tubulointerstitial lesion. This study aimed to assess the role of urinary biomarkers in predicting tubulointerstitial lesion and treatment response in FSGS patients.

Relationship between acute kidney injury before thoracic endovascular aneurysm repair and in-hospital outcomes in patients with type B acute aortic dissection

Objective Acute kidney injury (AKI) frequently occurs after catheter-based interventional procedures and increases mortality. However, the implications of AKI before thoracic endovascular aneurysm repair (TEVAR) of type B acute aortic dissection (AAD) remain unclear. This study evaluated the incidence, predictors, and in-hospital outcomes of AKI before TEVAR in patients with type B AAD. Methods Between 2009 and 2013, 76 patients were retrospectively evaluated who received TEVAR for type B AAD within 36 h from symptom onset. The patients were classified into no-AKI vs. AKI groups, and the severity of AKI was further staged according to kidney disease: improving global outcomes criteria before TEVAR. Results The incidence of preoperative AKI was 36.8%. In-hospital complications was significantly higher in patients with preoperative AKI compared with no-AKI (50.0% vs. 4.2%, respectively; P < 0.001), including acute renal failure (21.4% vs. 0, respectively; P < 0.001), and they increased with severity of AKI (P < 0.001). The maximum levels of body temperature and white blood cell count were significantly related to maximum serum creatinine level before TEVAR. Multivariate analysis showed that systolic blood pressure on admission (OR: 1.023; 95% CI: 1.003–1.044; P = 0.0238) and bilateral renal artery involvement (OR: 19.076; 95% CI: 1.914–190.164; P = 0.0120) were strong predictors of preoperative AKI. Conclusions Preoperative AKI frequently occurred in patients with type B AAD, and correlated with higher in-hospital complications and enhanced inflammatory reaction. Systolic blood pressure on admission and bilateral renal artery involvement were major risk factors for AKI before TEVAR.     

Urine Microscopy Is Associated with Severity and Worsening of Acute Kidney Injury in Hospitalized Patients

Background and objectives: Serum creatinine concentration at the time of nephrology consultation is not necessarily indicative of the severity of acute kidney injury (AKI). Although urine microscopy is useful to differentiate AKI, its role in predicting adverse clinical outcomes has not been well described.Design, setting, participants, & measurements: The relationship between urine microscopy findings at the time of nephrology consultation for AKI and clinical outcomes was evaluated prospectively. A urinary sediment scoring system was created on the basis of the number of renal tubular epithelial cells and granular casts. The primary outcome was worsening of AKI (progressing to higher AKI Network stage, dialysis, or death) during hospitalization.Results: Of 249 patients consulted for AKI, 197 had acute tubular necrosis or prerenal AKI and were included in the analysis. At consultation, 80 (40%) had stage 1, 53 (27%) had stage 2, and 66 (33%) had stage 3 AKI. The urinary sediment combined scores were lowest in those with stage 1 and highest in stage 3 AKI. Seventy-nine patients (40%) experienced worsening of AKI from the time of consultation. The urinary scoring system was significantly associated with increased risk of worsening AKI (adjusted relative risk: 7.3; 95% confidence interval: 4.5 to 9.7 for worsening with score of ≥3 versus score of 0) and was more predictive than AKI Network stage at the time of consultation.Conclusions: The urinary sediment score may be a useful tool to predict worsening of AKI due to either acute tubular necrosis or prerenal AKI during hospitalization.Currently, diagnosis of acute kidney injury (AKI) is based on serum creatinine concentration and urine output. The Acute Kidney Injury Network (AKIN) definition is based on these two parameters and uses various cutoffs to define three distinct AKI stages (1). Urine microscopy and biochemistry are complementary to these diagnostic parameters and provide information that facilitates the differentiation of AKI into traditional categories, including prerenal AKI and acute tubular necrosis (ATN), the most common causes of hospital-acquired AKI (2–4). Urinary microscopy in patients with ATN classically is described as containing renal tubular epithelial (RTE) cells, RTE cell casts, granular casts, or mixed cellular casts, whereas sediment in patients with prerenal AKI usually is bland or contains occasional hyaline casts (5–9). In fact, we recently demonstrated that urine microscopy at the time of nephrology consultation, on the basis of the number of RTE cells and granular casts (10). We believe this is important because both prognosis and therapies for prerenal AKI and ATN differ substantially, making early clinical differentiation fundamental to AKI management.

Table 1.

Scoring system based on number of granular casts and RTE cells

Urinary hepcidin-25 and risk of acute kidney injury following cardiopulmonary bypass

Summary

Background and objectives

Acute kidney injury (AKI) complicating cardiopulmonary bypass (CPB) results in increased morbidity and mortality. Urinary hepcidin-25 has been shown to be elevated in patients who do not develop AKI after CPB using semiquantitative mass spectrometry (SELDI TOF-MS). The goals of this study were to quantitatively validate these findings with ELISA and evaluate the diagnostic performance of hepcidin-25 for AKI.

Design, setting, participants, & measurements

A nested, case-control analysis of urinary hepcidin-25 in AKI (n = 22) and non-AKI (n = 22) patients was conducted to validate the SELDI TOF-MS data at the following times: preoperatively; the start of CPB; 1 hour on CPB; on arrival to the intensive care unit; and postoperative days (POD) 1 and 3 to 5. The diagnostic performance of hepcidin-25 was then evaluated in the entire prospective observational cohort (n = 338) at POD 1. AKI was defined as Cr >50% from baseline, within 72 hours postoperatively.

Results

Urinary hepcidin-25/Cr ratio was significantly elevated in all patients at POD 1 compared with baseline (P < 0.0005) and was also significantly elevated in non-AKI versus AKI patients at POD 1 (P < 0.0005). Increased log₁₀ hepcidin-25/Cr ratio was strongly associated with avoidance of AKI on univariate analysis. On multivariate analysis, the log₁₀ hepcidin-25/Cr ratio (P < 0.0001) was associated with avoidance of AKI with an area under the curve of 0.80, sensitivity 0.68, specificity 0.68, and negative predictive value 0.96.

Conclusions

Elevated urinary hepcidin-25 on POD 1 is a strong predictor of avoidance of AKI beyond postoperative day 1.     

Fractional excretion of sodium predicts worsening renal function in acute decompensated heart failure

BACKGROUND:

Renal impairment (RI), defined as an increase in creatinine level of greater than 26.5 mmol/L, develops in more than 30% of acute decompensated heart failure (ADHF) patients. Fractional excretion of sodium (FeNa) reflects sodium handling by the kidneys during diuresis.

AIM:

To study the relationship between FeNa and RI in patients admitted with ADHF.

METHOD:

The hospital course and renal function of all ADHF patients admitted to the hospital were prospectively observed. Patients were included if their admission creatinine level was 176 mmol/L or lower, they had been on a low-salt diet since admission, had urine sodium and creatinine samples collected more than 6 h after a furosemide dose in the first few days of admission, and they were on daily intravenous furosemide doses of 20 mg or more.

RESULTS:

Over six months, 51 patients met the inclusion criteria; the average daily dose of intravenous furosemide was 58.8 mg. RI developed in 39% of patients. A FeNa cut-off point of 0.4% was determined using ROC curve analysis; patients with a FeNa of greater than 0.4% (28 patients) were compared with patients with a lower FeNa (23 patients). Admission creatinine level and furosemide dose were higher in the first group (P=0.01 and P=0.06, respectively). The first group developed RI more frequently (OR=6.3; 95% CI 1.7 to 23.5; P=0.0047; adjusted OR for admission creatinine = 6.18; 95% CI 1.6 to 24.5; P=0.0096; and adjusted OR for furosemide dose = 4.7; 95% CI 1.3 to 16.7; P=0.016). They had a longer hospitalization course (median nine days [interquartile range 6.3 to 13.5 days] versus seven days [interquartile range 4.0 to 9.0 days]; P=0.036) and they were admitted to the cardiac care unit more frequently (OR=6.8; 95% CI 1.3 to 34.9; P=0.02).

CONCLUSION:

A FeNa of greater than 0.4% more than 6 h after a dose of diuretics predicts RI and a complicated hospital course in ADHF patients.     

Urinary Biomarkers in the Clinical Prognosis and Early Detection of Acute Kidney Injury

Background and objectives: Several novel urinary biomarkers have shown promise in the early detection and diagnostic evaluation of acute kidney injury (AKI). Clinicians have limited tools to determine which patients will progress to more severe forms of AKI at the time of serum creatinine increase. The diagnostic and prognostic utility of novel and traditional AKI biomarkers was evaluated during a prospective study of 123 adults undergoing cardiac surgery.Design, setting, participants, & measurements: Urinary neutrophil gelatinase-associated lipocalin (NGAL), cystatin C (CyC), kidney injury molecule-1 (KIM-1), hepatocyte growth factor (HGF), π-glutathione-S-transferase (π-GST), α-GST, and fractional excretions of sodium and urea were all measured at preoperative baseline, postoperatively, and at the time of the initial clinical diagnosis of AKI. Receiver operator characteristic curves were generated and the areas under the curve (AUCs) were compared.Results: Forty-six (37.4%) subjects developed AKI Network stage 1 AKI; 9 (7.3%) of whom progressed to stage 3. Preoperative KIM-1 and α-GST were able to predict the future development of stage 1 and stage 3 AKI. Urine CyC at intensive care unit (ICU) arrival best detected early stage 1 AKI (AUC = 0.70, P < 0.001); the 6-hour ICU NGAL (AUC = 0.88; P < 0.001) best detected early stage 3 AKI. π-GST best predicted the progression to stage 3 AKI at the time of creatinine increase (AUC = 0.86; P = 0.002).Conclusion: Urinary biomarkers may improve the ability to detect early AKI and determine the clinical prognosis of AKI at the time of diagnosis.Acute kidney injury (AKI) is a common and serious complication of cardiothoracic surgery (1); depending on the definition of AKI used, it may occur in over 40% of adults, with 1% to 5% requiring renal replacement therapy (RRT) (2–9). Recently, standardized clinical definitions of AKI have been implemented through the use of the RIFLE (Risk, Injury, Failure, Loss, and ESRD) and AKIN (Acute Kidney Injury Network) criteria (10,11). However, these criteria are still very much dependent on delayed serum creatinine elevations, the current gold standard for the diagnosis of AKI. Furthermore, as a functional marker of glomerular filtration, serum creatinine is not ideally suited to diagnose AKI caused by renal tubular injury, rather than reversible prerenal azotemia (10).In recent years, several novel human biomarkers have been demonstrated to detect acute tubular injury and have shown promise in their ability to precede and/or complement serum creatinine in the diagnosis of AKI (12–15). Cardiac surgery has long been used to study AKI because of the ability to prospectively follow patients before and after a well timed renal insult; for this reason, several urinary proteins have been shown to serve as biomarkers of AKI after cardiac surgery, including neutrophil gelatinase-associated lipocalin (NGAL) (16–20), cystatin C (CyC) (19,21), kidney injury molecule-1 (KIM-1) (18,21), interleukin-18 (IL-18) (22), and α-glutathione-S-transferase (α-GST) (23,24). Limited data are available comparing the ability of these markers to predict renal outcomes at the time of AKI diagnosis. In fact, nephrologists have limited tools in their arsenal to assess the presence and severity of renal tubular injury at the time of AKI diagnosis. Although urinalysis with microscopy has been shown to be of some utility in the differential diagnosis of AKI in a generalized hospital-based cohort (25), data supporting its use in the specific setting of cardiac surgery are lacking (24). Similarly, diagnostic mainstays of AKI evaluation such as the fractional excretion of sodium (FENa) have long been shown to be suboptimal tools in the complex setting of cardiac surgery AKI (24), in which volume status, fluid responsiveness, and diuretic use confound inferences regarding the relationship between tubular function and injury (26,27). Additionally, although recent data support the utility of the fractional excretion of urea (FEUrea) as a diagnostic tool in AKI (28), not all data support its use (29). Furthermore, very little is known about the utility of FENa or FEUrea compared with the novel urinary biomarkers discussed above for the differential diagnosis and prognostic evaluation of AKI.In this study, we assessed the diagnostic utility of urinary NGAL, CyC, KIM-1, hepatocyte growth factor (HGF), α-GST (a proximal tubular damage marker), π-GST (a marker specific to distal tubule damage), FENa, and FEUrea as biomarkers for the detection of early and severe AKI after adult cardiac surgery. These novel biomarkers can be thought of as falling into two categories: constitutive markers (proteins/enzymes that are normally present in renal tubular cells and not normally found in the urine in significant concentration but are released into the urine in direct response to cellular injury), and inducible biomarkers (proteins that are not normally found in high concentrations in renal tubular cells or urine until their production is directly upregulated in response to cellular injury). CyC, α-GST, and π-GST are constitutive proteins that are extruded into urine in the presence of site-specific renal tubular injury (CyC and α-GST are proximal and π-GST is distal); intracellular GSTs are released into urine by damaged tubular cells, whereas injured proximal tubules fail to reabsorb filtered CyC. In contrast, KIM-1 and NGAL are inducible biomarkers, gene products that are increased in direct response to nephron damage (30,31). We also evaluated the ability of these markers to predict the severity/stage of AKI at the time of clinical diagnosis by serum creatinine increase. We performed all of the above analyses for those subjects who developed AKI as defined by the AKIN (11). Recent data demonstrate that urine NGAL after cardiac surgery varies with baseline renal function (32); as such, a secondary analysis of baseline GFR was conducted for the aforementioned panel of biomarkers (32). Finally, we interpreted the data for all novel biomarker concentrations adjusted and unadjusted for dilution by indexing to urinary creatinine, but for brevity''s sake, we only report the indexed values unless otherwise noted.     

Neutrophil Gelatinase-Associated Lipocalin in the Diagnosis of Type 1 Cardio-Renal Syndrome in the General Ward

Summary

Background and objectives

The early identification of acute heart failure (HF) patients with type 1 cardio-renal syndrome should be the first step for developing prevention and treatment strategies for these patients. This study aimed to assess the performance of neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C in the early detection of type 1 cardio-renal syndrome in patients with acute HF.

Design, setting, participants, & measurements

One-hundred nineteen patients admitted with acute HF were studied. NGAL and creatinine were measured in the first hospitalization morning; creatinine was also measured at least after 48 to 72 hours. Physicians were blinded to NGAL and cystatin C levels. Type 1 cardio-renal syndrome was defined as an increase in the creatinine level of at least 0.3 mg/dl or 50% of basal creatinine.

Results

Type 1 cardio-renal syndrome developed within 48 to 72 hours in 14 patients (11.8%). Admission NGAL levels were higher in these patients: 212 versus 83 ng/dl. At a cutoff value of 170 ng/L, NGAL determined type 1 cardio-renal syndrome with a sensitivity of 100% and a specificity of 86.7%. The area under the receiver-operating characteristic curve of NGAL was 0.93 and that of cystatin C was 0.68.

Conclusions

Above a cutoff value of 170 ng/L, NGAL predicts 48- to 72-hour development of type 1 cardio-renal syndrome with a negative predictive value of 100% and a positive predictive value of 50%. NGAL independently associates with type 1 cardio-renal syndrome and might be a useful biomarker in the early recognition of these patients.     

Urinary Biomarkers and Renal Recovery in Critically Ill Patients with Renal Support

Summary

Background and objectives

Despite significant advances in the epidemiology of acute kidney injury (AKI), prognostication remains a major clinical challenge. Unfortunately, no reliable method to predict renal recovery exists. The discovery of biomarkers to aid in clinical risk prediction for recovery after AKI would represent a significant advance over current practice.

Design, setting, participants, & measurements

We conducted the Biological Markers of Recovery for the Kidney study as an ancillary to the Acute Renal Failure Trial Network study. Urine samples were collected on days 1, 7, and 14 from 76 patients who developed AKI and received renal replacement therapy (RRT) in the intensive care unit. We explored whether levels of urinary neutrophil gelatinase-associated lipocalin (uNGAL), urinary hepatocyte growth factor (uHGF), urinary cystatin C (uCystatin C), IL-18, neutrophil gelatinase-associated lipocalin/matrix metalloproteinase-9, and urine creatinine could predict subsequent renal recovery.

Results

We defined renal recovery as alive and free of dialysis at 60 days from the start of RRT. Patients who recovered had higher uCystatin C on day 1 (7.27 versus 6.60 ng/mg·creatinine) and lower uHGF on days 7 and 14 (2.97 versus 3.48 ng/mg·creatinine; 2.24 versus 3.40 ng/mg·creatinine). For predicting recovery, decreasing uNGAL and uHGF in the first 14 days was associated with greater odds of renal recovery. The most predictive model combined relative changes in biomarkers with clinical variables and resulted in an area under the receiver-operator characteristic curve of 0.94.

Conclusions

We showed that a panel of urine biomarkers can augment clinical risk prediction for recovery after AKI.     

Acute kidney injury in patients with cirrhosis of liver: Clinical profile and predictors of outcome

Background

Acute kidney injury (AKI) is a common complication of liver cirrhosis and is associated with poor survival. We studied the clinical profile and predictors of in-hospital mortality in patients with cirrhosis of the liver with AKI.

Methods

This retrospective cohort study examined patients at a tertiary care hospital. AKI staging was done based on the new 2015 Ascites Club Criteria. Patients were grouped into three types of AKI: pre-renal azotemia (PRA), hepatorenal syndrome (HRS), and acute tubular necrosis (ATN).

Results

Data of 123 patients with cirrhosis and AKI were analyzed. Most patients had AKI stage 3 (57.7%). ATN (42.3%) and HRS (43.9) were the predominant types of AKI followed by PRA (13.8%). The overall in-hospital mortality in our study was 44.7%. The mortality increased with increasing severity of AKI (p?=?0.0001) and was the highest in AKI stage 3 (p?=?0.001) and those who required hemodialysis (p?=?0.001). There was a significant in-hospital mortality in patients with ATN and HRS in comparison to PRA (p?=?0.001). On multivariate analysis, the factors predicting in-hospital mortality were AKI stage 3, and oliguria (p?=?0.0001).

Conclusions

Acute kidney injury in cirrhosis of liver carries high in-hospital mortality. Pre-renal AKI has a better survival compared to ATN and HRS. The higher stage of AKI at presentation and the presence of oliguria are two important predictors of in-hospital mortality.