New insights in glomerular filtration rate formulas and chronic kidney disease classification

BackgroundThe MDRD Study equation is the most popular equation for estimating the glomerular filtration rate (eGFR) from serum creatinine (Scr), age, sex and race. Many articles deal with ethnic factors, correcting the MDRD Study equation for different populations, with more or less success. The new CKD-EPI equation introduced the concept of a population-normalized Scr in the eGFR equation for white men (Scr/0.90) and white women (Scr/0.70).MethodsWe introduce alternative mathematical forms for the MDRD Study equation and the CKD-EPI equation, using the concept of a population-normalized Scr, resulting in a more general and mathematically less complicated form for the eGFR equation.ResultsWe show that the normalization constant corresponds to the mean Scr-value for the specific healthy population. We compared the established equations with the new alternative forms, and show that the differences are minimal. The sex/race dependency is completely comprehended in the normalization constant, making the alternative eGFR equations independent of sex and race.ConclusionThe age-dependency of eGFR remains and consequently age-dependent cutoff values for the classification of Chronic Kidney Disease (CKD) look more appropriate, contrary to the current classification rules. The population-normalized Scr which is independent of age, sex and race may serve as an alternative for the classification of CKD.     

Comparison of modification of diet in renal disease and chronic kidney disease epidemiology collaboration formulas in predicting long-term outcomes in patients undergoing stent implantation due to stable coronary artery disease

Introduction

The aim was to assess the predictive value of estimated glomerular filtration rate (eGFR) using two formulas: modification of diet in renal disease (MDRD) and chronic kidney disease epidemiology collaboration (CKD-EPI), in a population with stable coronary artery disease (SCAD) undergoing percutaneous coronary revascularization (PCI).

Methods

The analyzed cohort included 3,141 consecutive patients with SCAD who underwent PCI, between January 2006 and December 2011. Follow-up data were available for 3,123 (99.4 %) patients.

Results

The median follow-up was 1,127 days (interquartile range 566–1,634 days). During the observation period, 330 deaths were reported. In patients with serum creatinine (S-Cr) within normal range, eGFR by CKD-EPI equation predicted long-term outcome more accurately, than eGFR by MDRD formula—continuous Net Reclassification Improvement: 0.296 (95 % CI, 0.08–0.5 p = 0.03). In patients with elevated S-CR, eGFR calculated by both formulae had similar efficacy in assessing death risk. After adjustment for differences in clinical characteristics, both formulae were associated with mortality, but only in patients with elevated S-Cr: eGFR by MDRD (per 10 ml/min/1.73 m²) HR: 0.74 [95 % CI, 0.61–0.89, p = 0.002], eGFR by CKD-EPI (per 10 ml/min/1.73 m²) HR: 0.75 (95 % CI, 0.63–0.89, p = 0.001). After adjustment for covariates, eGFR by CKD-EPI equation did not offer more appropriate categorization of individuals with respect to long-term mortality.

Conclusion

Our results indicate that in multivariable analysis eGFR calculated by MDRD and CKD-EPI equations has similar predictive value. In a population of patients with SCAD and S-Cr within normal range, eGFR calculated by CKD-EPI equation outperforms eGFR calculated by MDRD equation in assessing death risk.     

Estimating glomerular filtration rate (GFR) in diabetes: The performance of MDRD and CKD-EPI equations in patients with various degrees of albuminuria

Objectives

The aim of this study was to compare the performance of Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and Modification of Diet in Renal Disease Study (MDRD) equations in estimating GFR in a large cohort of diabetic patients with various degrees of albuminuria.

Design and methods

In a group of 842 diabetic patients GFR was estimated from standardized creatinine, with MDRD-Study and CKD-EPI equations, and their performance evaluated regarding clinical stages of albuminuria and chronic kidney disease (CKD).

Results

Patients with normoalbuminuria had higher eGFR when calculated by CKD-EPI, than MDRD-Study equation [median (IQR): 103 (91–115) vs 97 (85–113) mL/min/1.73 m², P = 0.006, n = 364], which significantly influenced the prevalence of stage 1 CKD [eGFR > 90 mL/min/1.73 m²: 76.7% (CKD-EPI) vs. 65.1% (MDRD-Study), P = 0.005]. There were no differences between the eGFR values derived by two equations in patients with micro- and macroalbuminuria, and more advanced staging of CKD.

Conclusion

CKD-EPI equation might be a superior surrogate marker of GFR in patients with normoalbuminuria and hyperfiltration and could be used as a screening tool for early renal impairment in diabetes. It's validity as a marker of progression of diabetic nephropathy merits further investigation.     

A new tool for predicting the probability of chronic kidney disease from a specific value of estimated GFR

Abstract

Objective. To demonstrate how patients’ probability of having chronic kidney disease (CKD) stage 3–5 (measured GFR <60 mL/min/1.73 m²) can be predicted from a specific value of estimated glomerular filtration rate (eGFR). Material and methods. The probability of CKD stage 3–5 was predicted from a logistic regression model (n = 850) using three different eGFR prediction equations: Lund-Malmö, MDRD and CKD-EPI. Population weighting was used to illustrate how this probability varies in three different populations: original sample (55% true prevalence of CKD stage 3–5), a screening (6.7% prevalence) and a CKD population (84% prevalence). Results. All three eGFR-equations had high classification ability (area under the receiver-operating-characteristic curve = 97%). The probability of CKD stage 3–5 increased with decreasing eGFR, varied substantially among the populations studied and to some extent between the eGFR-equations. Using the Lund-Malmö equation as illustration, the probability of CKD stage 3–5 is > 90% only when eGFR is <38 mL/min/1.73 m² in a screening population, whereas it is > 90% already when eGFR is <51 mL/min/1.73 m² in a CKD population. Conversely, the probability of CKD stage 3–5 is <10% if eGFR > 59 mL/min/1.73 m² in a screening population, whereas it is <10% only when eGFR is > 88 mL/min/1.73 m² in a CKD population. Conclusion. Instead of reporting diagnostic accuracy as sensitivity, specificity, and predictive values, actual eGFR supplemented with the probability that it represents a true GFR <60 mL/min/1.73 m² may be more valuable for physicians. Clinical (pre-test) probability in the population must be considered when predicting this probability.     

Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation pronouncedly underestimates glomerular filtration rate in type 2 diabetes

OBJECTIVE To evaluate the performance of the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation to estimate glomerular filtration rate (GFR) in type 2 diabetic patients with GFR >60 mL/min/1.73 m(2). RESEARCH DESIGN AND METHODS This was a cross-sectional study including 105 type 2 diabetic patients. GFR was measured by (51)Cr-EDTA method and estimated by the MDRD and CKD-EPI equations. Serum creatinine was measured by the traceable Jaffe method. Bland-Altman plots were used. Bias, accuracy (P30), and precision were evaluated. RESULTS The mean age of patients was 57 ± 8 years; 53 (50%) were men and 90 (86%) were white. Forty-six (44%) patients had microalbuminuria, and 14 (13%) had macroalbuminuria. (51)Cr-EDTA GFR was 103 ± 23, CKD-EPI GFR was 83 ± 15, and MDRD-GFR was 78 ± 17 mL/min/1.73 m2 (P < 0.001). Accuracy (95% CI) was 67% (58-74) for CKD-EPI and 64% (56-75) for MDRD. Precision was 21 and 22, respectively. CONCLUSIONS The CKD-EPI and MDRD equations pronouncedly underestimated GFR in type 2 diabetic patients.     

Applicability of estimated glomerular filtration rate in stratifying chronic kidney disease

Objective. The aim of this audit was to evaluate the degree of glomerular filtration rate (GFR) among inpatients and outpatients in a District General Hospital, with special attention given to laboratory testing and impact on health delivery. Background. UK Chronic Kidney Disease guidelines recommend that investigation of renal function should be accompanied by an estimation of GFR (eGFR) in order to identify and manage patients with chronic kidney disease (CKD). The estimated GFR forms the basis for classification of CKD and appropriate action plans for patient management and follow‐up. Method. A retrospective audit of 8160 results from a predominantly British Caucasian population was carried out; extracting creatinine results from two isolated months in years 2001 and 2004. The estimated GFR (eGFR) was calculated using the MDRD formula. The data were classified according to demography, serum creatinine and eGFR. Patients from the 2001 database were classified according to eGFR and those with a value of <60?mL/min/1.73m² were followed up in 2004. Results. The difference in eGFR between the men and women was significantly different with medians (confidence intervals) of 80.1 (41–109) and 64.4 (30–84.6) (p<0.0001), respectively. There was an inverse association between age and eGFR in both genders (p<0.0001), with a decrease in eGFR of around 7?% for each decade increase in age. 1926 patients (24?%) of results studied had eGFR <60?mL/min, of whom 64?% were females and 36?% males. Follow‐up of patients with eGFR<60?mL/min from 2001 showed that 4?% progressed to stages 4 and 5 CKD. Conclusion. eGFR is inversely associated with increasing age and female gender. MDRD derived eGFR fails to completely compensate for age and gender variations and thus different action limits may be required. Small but significant numbers of patients progressed to stages 4 and 5 CKD. Additional clarity in describing “progressive fall in eGFR” in the guidelines would improve identification of the population most at risk.     

Assessment of the CKD-EPI equation to estimate glomerular filtration rate in adults from a Chinese CKD population

The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation was introduced to estimate glomerular filtration rate (GFR) in chronic kidney disease (CKD) patients based on serum creatinine. The CKD-EPI equation shows better accuracy compared with the current gold standard equation, the Modification of Diet in Renal Disease (MDRD) equation, but it has not been externally validated in Chinese patients. This study compared the CKD-EPI equation with the original MDRD equation and two Chinese MDRD-based equations for estimating GFR in 200 Chinese CKD patients. The (99m)Tc-diethylenetriamine penta-acetate ((99m)Tc-DTPA) method was used to determine actual GFR. The CKD-EPI equation produced GFR estimates that were more consistent with the (99m)Tc-DTPA GFR than did the MDRD equations. The precision and accuracy of the CKD-EPI equation were significantly higher than those of the MDRD equations. In conclusion, the CKD-EPI equation was superior to the existing MDRD equations in terms of estimating GFR and we recommend its clinical use in Chinese CKD patients.     

健康人群和慢性肾病患者基于血清CysC水平估算肾小球滤过率公式的适用性评价

目的 评价基于血清胱抑素C(Cys C)的估算肾小球滤过率(eGFR)公式在健康人群和慢性肾病(CKD)患者中的适用性。方法 选取2 495例健康人和805例CKD患者作为研究对象,测定其血清Cys C和肌酐(Cr),使用改善全球肾脏病预后组织(KDIGO)慢性肾脏病评估与管理临床实践指南推荐的公式(2012 CKD-EPIcr-cysc,2012CKD-EPIcysc)和笔者实验室建立的基于Cys C的公式(eGFRcysc)分别计算研究对象的eGFR。以KDIGO推荐的公式为参考,用偏倚、偏倚的四分位数间距(IQR)和P30评价eGFRcysc的性能。结果 健康人群的Cys C和Cr的M(P25,P75)分别为0.76(0.67,0.86)mg/L和64.1(53.8,75.6)μmol/L。CKD患者的Cys C和Cr的M(P25,P75)分别为4.18(1.99,5.93)mg/L和385.4(152.1,704.5)μmol/L。在健康人群和CKD的1～4期患者中,eGFRcysc与2012 CKD-EPIcr-cysc的偏倚均小于2012CKD-EPIcysc的偏倚。在所有研究对象中,IQR是较低的(2.0～13.3)。在健康人群和CKD的1～2期患者中,P30均达到90%以上。Bland-Altman分析结果显示,在所有研究对象中,偏倚的一致限在-30～30范围内,一致限内的比例均大于90%。在CKD分期方面,eGFRcysc与2012 CKD-EPIcr-cysc具有中等的一致性(κ=0.487)。结论 在评价健康人群、1期CKD患者和2期CKD患者的GFR时,eGFRcysc与2012 CKD-EPIcr-cysc具有较好的一致性。在评价3～5期CKD患者的GFR时,与2012 CKD-EPIcr-cysc比较,eGFRcysc会高估GFR。在1～3期CKD患者中,eGFRcysc与2012 CKD-EPIcr-cysc具有较好的分期一致性,在4～5期CKD患者中,分期一致性较差。     

Estimated glomerular filtration rate (eGFRCystC) from serum cystatin C shows strong agreement with iohexol clearance in patients with low GFR

Objective. Estimation of glomerular filtration rate (eGFR) is essential in the diagnosis and monitoring of patients with kidney disease and for correct dosage of drugs eliminated from the circulation by the kidneys. Cystatin C has been shown in several studies to be superior to creatinine in estimating eGFR. However, there are few studies on the performance of cystatin C estimated eGFR (eGFR_CystC) in patients with advanced kidney disease and low GFR. Material and methods. We measured serum cystatin C, together with serum creatinine, during iohexol clearance in patients with iohexol clearance below 30?mL/min/1.73?m². The cystatin C values were used to calculate eGFR_CystC using the formula eGFR (mL/min/1.73m²) = 79.901*(cystatin C value in mg/L)^?1.4389. Results. There was good correlation between eGFR_CystC and iohexol clearance (r = 0.88) in patients with iohexol clearance <30?mL/min/1.73?m² and none of the patients had a difference between eGFR_CystC and iohexol clearance exceeding 50?%. The Modification of Diet in Renal Disease (MDRD) equation and corrected MDRD eGFR showed a positive bias and weaker correlations with iohexol eGFR (MDRD = 5.32+1.22*iohexol clearance; corrected MDRD = 4.76+1.10*iohexol clearance; r = 0.59). For MDRD eGFR, 42 of 94 (44.7?%) samples showed more than 50?% difference to iohexol clearance. Conclusions. eGFR_CystC is an efficient, practical and cost‐effective alternative to iohexol clearance in patients with reduced GFR.     

Classification of chronic kidney disease by estimated glomerular filtration rate

Background Serum creatinine concentration alone as a marker of kidney function is inadequate. Thus several equations for estimating glomerular filtration rate (eGFR) have been proposed within the last years. Patients and methods In our study we compared three frequently used equations, the abbreviated modification of diet in renal disease (MDRD) formula, the extended MDRD formula and the recently proposed Mayo clinic equation in a large patient cohort. Results A total of 244 507 patients attending the Vienna General Hospital were evaluated for their kidney function and three equations for eGFR were compared. The median age of the patients was 51 years (ranging from 18·0 to 102·6 years) with 44·3% males (n = 108 527). We observed a significant increase of patients with eGFR classes four and five (according to Kidney Disease Outcomes Quality Initiative (K/DOQI) guidelines) with advanced age. Whereas approximately 1% of patients < 30 years presented with eGFR classes four and five (defined as eGFR < 30 mL min^?1 1·73 m^?2), this prevalence increased up to ～12% in patients at the age of 80 years or older. All three equations showed comparable results for eGFR classes four and five. The proportion of patients with mild to moderate impairment of kidney function is higher using both MDRD equations. Conclusions The MDRD equations (particularly the abbreviated MDRD formula) result in considerably higher rates of eGFR classes two and three compared to the Mayo Clinic equation, while all three were comparable in classes four and five. This should be considered when eGFR is used in the diagnosis of chronic kidney disease.     

Performance of the chronic kidney disease epidemiology collaboration equation to estimate glomerular filtration rate in diabetic patients

OBJECTIVE

The best method to estimate glomerular filtration rate (GFR) in diabetic patients is still largely debated. We compared the performance of creatinine-based formulas in a European diabetic population.

RESEARCH DESIGN AND METHODS

We compared the performance of Cockcroft and Gault, simplified Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology (CKD-EPI) Collaboration equations in 246 diabetic patients by calculating the mean bias and the interquartile range (IQR) of the bias, 10% (P10) and 30% (P30) accuracies, and Bland-Altman plots. GFR was measured by inulin clearance.

RESULTS

For the whole population, the IQR was slightly lower for CKD-EPI, but the mean bias was lower and P10 and P30 were higher for MDRD. Similar results were observed in specific subgroups, including patients with mild renal insufficiency, obese patients, or type 2 diabetic patients.

CONCLUSIONS

In our population, the CKD-EPI formula does not exhibit better performance than the simplified MDRD formula for estimating GFR.Using a creatinine-based formula is the most common way to evaluate the glomerular filtration rate (GFR) in clinical practice. However, it can lead to an inaccurate evaluation, especially in patients with normal renal function (1). A new GFR formula, the Chronic Kidney Disease Epidemiology (CKD-EPI) Collaboration equation, has recently been developed and has exhibited better performance than the other creatinine-based formulas in the general population (2). Therefore, we compared the performance of the CKD-EPI equation to Cockcroft and Gault (CG) and simplified Modification of Diet in Renal Disease (MDRD) equations in a population of diabetic patients.     

Estimating kidney function and use of oral antidiabetic drugs in elderly

The prevalence of diabetes mellitus (DM) and renal impairment rises with age making regular estimation of glomerular filtration rate (eGFR) in older diabetics necessary. This study investigated the differences among available estimating equations in assessing eGFR in older diabetics and examined the use of oral antidiabetic drugs (OADs) in relation to renal function. Patients with DM were participants of the Berlin Initiative Study (BIS), a population‐based cohort study initiated in 2009 in Berlin, Germany, to evaluate kidney function in people ≥70 years. GFR was estimated with the creatinine‐based CKD‐EPI_CREA (Chronic Kidney Disease Epidemiology Collaboration), the MDRD (Modification of Diet in Renal Diseases) and the BIS1 equation and was directly measured (mGFR) with iohexol clearance as a gold standard in a subgroup (n = 137). Creatinine clearance was estimated with the Cockcroft–Gault equation (CrCl). DM prevalence was 26% (539 of 2070 overall participants). The antidiabetic drugs most commonly used among OAD patients were metformin (67%), glimepiride (27%) and glibenclamide (14%). Three of ten metformin patients had a CrCl <60 mL/min. Compared to mGFR, the mean differences of filtration rates calculated by MDRD, CKD‐EPI_CREA and BIS1 were +8.9, +6.7 and ?1.8 mL/min/1.73 m², respectively. Summing up, many patients with a CrCl <60 mL/min received metformin, although this represents a contraindication in Germany. Glibenclamide was commonly used despite its classification as potentially inappropriate medication in older adults. Finally, BIS1 performed better in estimating GFR in older diabetics than MDRD or CKD‐EPI_CREA.     

Clinical utility of creatinine- and cystatin C-based definition of renal function for risk prediction of primary cardiovascular events in patients with diabetes

OBJECTIVE

To assess the cardiovascular risk of diabetic subjects with chronic kidney disease (CKD) based on different estimated glomerular filtration rate (eGFR) equations and to evaluate which definition of CKD best improves cardiovascular risk prediction of the Framingham Cardiovascular Risk Score (Framingham-CV-RS).

RESEARCH DESIGN AND METHODS

CKD was defined as eGFR <60 mL/min/1.73 m², estimated by the creatinine-based Modification of Diet in Renal Disease (MDRD) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations and a cystatin C–based equation (CKD-CysC). Cox regression was used to estimate hazard ratios (HRs) of subjects with CKD for incident cardiovascular events in a cohort of 1,153 individuals with diabetes (baseline age 50–74 years). Furthermore, the CKD definitions were added individually to a reference model comprising the Framingham-CV-RS variables and HbA_1c, and measures of model discrimination and reclassification were assessed.

RESULTS

During 5 years of follow-up, 95 individuals had a primary cardiovascular event. Crude HRs were increased for all CKD definitions. However, after adjusting for established cardiovascular risk factors, HRs for both creatinine-based CKD definitions were attenuated to point estimates of 1.03, whereas the HRs for the cystatin C–based CKD definition remained significantly increased (HR 1.75 [95% CI 1.07–2.87]). Extension of the reference model by the different CKD definitions resulted in an increase in the c statistic only when adding CKD-CysC (from 0.638 to 0.644) along with a net reclassification improvement of 8.9%.

CONCLUSIONS

Only the cystatin C–based CKD definition was an independent risk predictor for cardiovascular events in our diabetic study cohort and indicated a potentially better clinical utility for cardiovascular risk prediction than creatinine-based equations.Chronic kidney disease (CKD) is a frequent disease in the elderly, especially among older adults with diabetes (1,2). However, epidemiologic data about the prevalence of CKD in patients with diabetes remain sparse and the accuracy of the different estimating equations to assess renal function in clinical routine is still debated (1,3,4).CKD can be classified with an estimated glomerular filtration rate (eGFR) of <60 mL/min/1.73 m² (CKD stages 3–5) (5). The most commonly used equation to estimate glomerular filtration rate (GFR) is the serum creatinine–based abbreviated Modification of Diet in Renal Disease (MDRD) equation (6), although it is well known that it underestimates GFR in the normal and high-normal range (7). Recently, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation has been introduced as a better means of estimate eGFR in observational research (8). However, data from patients with diabetes comparing the CKD-EPI and MDRD equations are still limited (8). Performance of creatinine-based eGFR in patients with diabetes and nephropathy lacks accuracy to monitor kidney function (9), especially in the early phases of renal impairment, and it can take years until other signs of a glomerulopathy such as albuminuria appear (10). Therefore, cystatin C–based estimating equations are suggested to show better clinical utility compared with creatinine-based equations (11,12).Which formula is best to be used to classify CKD in subjects with diabetes is an important question, especially because effective interventions exist to reduce the risk for cardiovascular disease and progression to end-stage renal disease (13). However, no study thus far has compared the MDRD and CKD-EPI formulas with a cystatin C–based equation in patients with diabetes (14). An eligible end point to shed further light on this question is an estimated predictive value of each equation for cardiovascular disease because CKD is clearly associated with cardiovascular end points, independent of established cardiovascular risk factors (15,16).Therefore, the objective of this analysis is to estimate the prognostic utility of serum creatinine– and cystatin C–based CKD definitions for incident cardiovascular events in subjects with diabetes.     

Evaluation of creatinine,cystatin C and eGFR by different equations in professional cyclists during the Giro d'Italia 3-weeks stage race

Abstract

In this study, creatinine-based equations to evaluate glomerular filtration rate (eGFR) were proposed to more accurately assess kidney function, and cystatin C, a parameter not dependent on muscular mass, was introduced to improve GFR calculation in professional cyclists during a long-lasting race. Nine cyclists participating in the 2011 Giro d'Italia were recruited. Blood and anthropometrical data were collected the day before (T ? 1) the race, on the 12th day (T 12) and on the 22nd day (T 22) of the race. Haemoglobin and haematocrit were registered. Haemodilution was observed at T 12, whilst stabilization was evident at T 22. Creatinine, cystatin C concentrations and eGFR values were not modified during the observed period; only GFR evaluated with the Cockcroft-Gault (CG) formula and expressed as ml/min/1.73 m² significantly decreased (p < 0.05) at T 22 in comparison with T ? 1, probably as a consequence of weight decrease. Cystatin C levels were in the reference range, while creatinine concentrations were lower. The lowest eGFR values were observed with CG normalized and the Modification of Diet in Renal Disease (MDRD) formulas. A good correlation was observed between the MDRD and the Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) equations and between CG normalized and both CKD-EPI and MDRD formulas. The worst correlation was registered between CKD-EPI creatinine and cystatin C and all the other equations. In conclusion, adaptive mechanisms of renal function allow athletes to maintain stable creatinine, cystatin C and eGFR values during a long-lasting race. The use of GFR equations to evaluate general health status of sportsmen should be recommended with caution, considering also weight modification during competition.     

6种基于血肌酐的肾小球滤过率估算公式在健康人群中的应用评估

目的评价基于酶法和苦味酸速率法的血清肌酐的6种估算的肾小球滤过率（eGFR）公式在表观健康人群中的适用性。方法从健康体检人群中筛选出694名表观健康人,分别用酶学方法和碱性苦味酸速率法检测血清肌酐,通过6种eGFR公式[Cockcroft—Gault（C—G）公式、简化肾脏病膳食改善（MDRD）公式、MDRD-中国人公式、同位素稀释质谱法（IDMS）-MDRD公式、慢性肾脏病流行病合作组（CKD-EPI）公式和EPI-亚洲人（EPI-Asian）公式]分别计算其eGFR并进行比较。结果694名表观健康人群的血肌酐检测结果分别为酶法（65．8±13．3）μmolfL（范围为36～117μmol／L）,苦味酸速率法（83．0±12．7）μmol／L（范围为57～131μmol／L）。以eGFR值男性85—125mL／min、女性75—115mL／min作为参考区间,基于酶法检测肌酐的eGFR值在表观健康人群中的适用性依次为CKD—EPI公式（72．3％）〉IDMS—MDRD公式（69．9％）〉简化MDRD公式（61．3％）〉EPI—Asian公式（60．7％）〉C—G公式（54．8％）〉MDRD一中国人公式（27．3％）（P〈0．05）,IDMS—MDRD公式在男、女性之间的适用性差异最小（仅相差1．6％）;基于苦味酸速率法检测肌酐的eGFR值在表观健康人群中的适用性依次为MDRD一中国人公式（80．0％）〉EPI—Asian公式（70．1％）〉CKD—EPI公式（63．8％％）〉简化MDRD公式（59．1％）〉C—G公式（52．4％）〉IDMS—MDRD公式（40．7％）（P〈0．05）,MDRD-中国人公式在男、女性之间的适用性差异最小（仅相差1％）。结论以上6种eGFR公式计算结果有明显差异。如果用溯源至IDMS的酶法检测血清肌酐,可选用CKD—EPI公式、IDMS—MDRD公式来评价中国北方健康人群的eGFR;如果用苦味酸速率法检测血清肌酐,可选用MDRD-中国人公式来评价中国北方健康人群的eGFR。     

Low rates of automatic reporting of estimated glomerular filtration rate in Southern Brazilian laboratories

ObjectivesThe aim of this study was to evaluate the rate of eGFR reporting in Southern Brazilian laboratories.Design and methodsThe eGFR automatic reporting, as assessed by Modification of Diet in Renal Disease (MDRD) and/or Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine-based equations, was evaluated in a representative cross-sectional sample. A standardized questionnaire to obtain this information was given out by mail or email.ResultsFive-hundred fifty laboratories, evenly distributed in the different state regions, completed the questionnaire. The eGFR was automatically reported by 54 (9.8%) laboratories, and the MDRD was the most commonly used equation (94.5%). The Jaffe methods were the most employed technique (94%) to measure serum creatinine.ConclusionThe automatic eGFR reporting rate was unacceptably low, emphasizing the crucial role of educating medical teams and laboratories on the importance of having these tools available to optimize detection of renal disease and proper treatment.     

Reference intervals for serum creatinine with enzymatic assay and evaluation of four equations to estimate glomerular filtration rate in a healthy Chinese adult population

BackgroundWith the wide usage of enzymatic assays to determine serum creatinine (Scr) in China, reference interval (RI) needs to be established. At the same time, the performance of Scr based equations to calculate estimated glomerular filtration rate (eGFR) in healthy Chinese adults has not been extensively investigated.MethodsThis study has strictly followed the International Federation of Clinical Chemistry (IFCC) recommendations and the Clinical Laboratory Standards Institute (CLSI) C28-A2 document. A total number of 778 healthy Chinese adults (male 433, female 345) were enrolled in this study.ResultsBy nonparametric method, RIs for males were: < 60 years, 58–93 μmol/l and > 60 years, 54–109 μmol/l; RIs for females were: < 60 years, 42–69 μmol/l and > 60 years, 43–83 μmol/l. Modification of Diet in Renal Disease (MDRD) equation and MDRD for Japanese made the percentage of eGFR > 90 ml/min/1.73 m² 31.7% and 4.9%; percentage of eGFR 60–89 ml/min/1.73 m² 65.2% and 64.0%, respectively. Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation and CKD-EPI for Asian made the percentage of eGFR > 90 ml/min/1.73 m² 89.2% and 94.0%; percentage of eGFR 60–89 ml/min/1.73 m² 10.3% and 5.7%, respectively.ConclusionScr RIs of healthy Chinese adults were found to be lower than those of Caucasians. Two MDRD equations underestimated GFR, while two CKD-EPI equations seemed to estimate a reasonable distribution of eGFR in healthy Chinese adult populations.     

Applicability of estimated glomerular filtration rate in stratifying chronic kidney disease

OBJECTIVE: The aim of this audit was to evaluate the degree of glomerular filtration rate (GFR) among inpatients and outpatients in a District General Hospital, with special attention given to laboratory testing and impact on health delivery. BACKGROUND: UK Chronic Kidney Disease guidelines recommend that investigation of renal function should be accompanied by an estimation of GFR (eGFR) in order to identify and manage patients with chronic kidney disease (CKD). The estimated GFR forms the basis for classification of CKD and appropriate action plans for patient management and follow-up. METHOD: A retrospective audit of 8160 results from a predominantly British Caucasian population was carried out; extracting creatinine results from two isolated months in years 2001 and 2004. The estimated GFR (eGFR) was calculated using the MDRD formula. The data were classified according to demography, serum creatinine and eGFR. Patients from the 2001 database were classified according to eGFR and those with a value of <60 mL/min/1.73 m(2) were followed up in 2004. RESULTS: The difference in eGFR between the men and women was significantly different with medians (confidence intervals) of 80.1 (41-109) and 64.4 (30-84.6) (p<0.0001), respectively. There was an inverse association between age and eGFR in both genders (p<0.0001), with a decrease in eGFR of around 7 % for each decade increase in age. 1926 patients (24 %) of results studied had eGFR <60 mL/min, of whom 64 % were females and 36 % males. Follow-up of patients with eGFR<60 mL/min from 2001 showed that 4 % progressed to stages 4 and 5 CKD. CONCLUSION: eGFR is inversely associated with increasing age and female gender. MDRD derived eGFR fails to completely compensate for age and gender variations and thus different action limits may be required. Small but significant numbers of patients progressed to stages 4 and 5 CKD. Additional clarity in describing "progressive fall in eGFR" in the guidelines would improve identification of the population most at risk.     

Estimated glomerular filtration rate (eGFRCystC) from serum cystatin C shows strong agreement with iohexol clearance in patients with low GFR

OBJECTIVE: Estimation of glomerular filtration rate (eGFR) is essential in the diagnosis and monitoring of patients with kidney disease and for correct dosage of drugs eliminated from the circulation by the kidneys. Cystatin C has been shown in several studies to be superior to creatinine in estimating eGFR. However, there are few studies on the performance of cystatin C estimated eGFR (eGFRCystC) in patients with advanced kidney disease and low GFR. MATERIAL AND METHODS: We measured serum cystatin C, together with serum creatinine, during iohexol clearance in patients with iohexol clearance below 30 mL/min/1.73 m2. The cystatin C values were used to calculate eGFRCystC using the formula eGFR (mL/min/1.73 m2) = 79.901*(cystatin C value in mg/L)-1.4389. RESULTS: There was good correlation between eGFRCystC and iohexol clearance (r = 0.88) in patients with iohexol clearance <30 mL/min/1.73 m2 and none of the patients had a difference between eGFRCystC and iohexol clearance exceeding 50 %. The Modification of Diet in Renal Disease (MDRD) equation and corrected MDRD eGFR showed a positive bias and weaker correlations with iohexol eGFR (MDRD = 5.32+1.22*iohexol clearance; corrected MDRD = 4.76+1.10*iohexol clearance; r = 0.59). For MDRD eGFR, 42 of 94 (44.7%) samples showed more than 50% difference to iohexol clearance. CONCLUSIONS: eGFRCystC is an efficient, practical and cost-effective alternative to iohexol clearance in patients with reduced GFR.     

A Foot Ergometer for Graded Muscular Exercise

Objective: In 2002, a uniform definition of chronic kidney disease (CKD) became widely accepted. The level of glomerular filtration rate (GFR) is the pivot for staging the disease. Because GFR is not readily measured in routine clinical practice, statistical models such as the Modification of Diet in Renal Disease (MDRD) equation have been proposed for estimating GFR. The MDRD equation is gaining worldwide acceptance in assisting the diagnosis and staging of CKD. Material and methods: We use theoretical and experimental considerations based on serum creatinine (Scr) measurements obtained with an enzymatic IDMS-traceable assay and compare CKD classifications based on Scr alone with classifications based on the eGFR-MDRD and eGFR-Mayo Clinic equations. Results: Based on recently published reference intervals for enzymatically determined Scr, we show that eGFR-MDRD<60 mL/min/1.73m² corresponds extremely well with Scr>upper reference limit. The different CKD stages III, IV and V can be redefined using Scr alone, resulting in 97.5% agreement. Conclusion: We show that neither the MDRD study equation nor the Mayo Clinic equation add extra value to the information already contained in Scr itself. Because of the limited applicability of the eGFR equations, Scr has even more potential to assist in the diagnosis and classification of CKD than eGFR-MDRD.