Cystatin C is a more sensitive marker than creatinine for the estimation of GFR in type 2 diabetic patients

BACKGROUND: Glomerular filtration rate (GFR) is the best overall index of renal function in health and disease. Inulin and 51Cr-EDTA plasma clearances are considered the gold standard methods for estimating GFR. Unfortunately, these methods require specialized technical personnel over a period of several hours and high costs. In clinical practice, serum creatinine is the most widely used index for the noninvasive assessment of GFR. Despite its specificity, serum creatinine demonstrates an inadequate sensitivity, particularly in the early stages of renal impairment. Recently, cystatin C, a low molecular mass plasma protein freely filtered through the glomerulus and almost completely reabsorbed and catabolized by tubular cells, has been proposed as a new and very sensitive serum marker of changes in GFR. This study was designed to test whether serum cystatin C can replace serum creatinine for the early assessment of nephropathy in patients with type 2 diabetes. METHODS: The study was performed on 52 Caucasian type 2 diabetic patients. Patients with an abnormal albumin excretion rate (AER) were carefully examined to rule out non-diabetic renal diseases by ultrasonography, urine bacteriology, microscopic urine analysis, and kidney biopsy. Serum creatinine, serum cystatin C, AER, serum lipids, and glycosylated hemoglobin (HbA1c) were measured. GFR was estimated by the plasma clearance of 51Cr-EDTA. In addition the Cockcroft and Gault formula (Cockcroft and Gault estimated GFR) was calculated. RESULTS: Cystatin C serum concentration progressively increased as GFR decreased. The overall relationship between the reciprocal cystatin C and GFR was significantly stronger (r = 0.84) than those between serum creatinine and GFR (r = 0.65) and between Cockcroft and Gault estimated GFR and GFR (r = 0.70). As GFR decreased from 120 to 20 mL/min/1.73 m2, cystatin C increased more significantly that serum creatinine, giving a stronger signal in comparison to that of creatinine over the range of the measured GFR. The maximum diagnostic accuracy of serum cystatin C (90%) was significantly better than those of serum creatinine (77%) and Cockcroft and Gault estimated GFR (85%) in discriminating between type 2 diabetic patients with normal GFR (>80 mL/min per 1.73 m2) and those with reduced GFR (<80 mL/min/1.73 m2). In particular, the cystatin C cut-off limit of 0.93 mg/L corresponded to a false-positive rate of 7.7% and to a false-negative rate of 1.9%; the serum creatinine cut-off limit of 87.5 micromol/L corresponded to a false-positive rate of 5.8% and to a false-negative rate of 17.0%. CONCLUSIONS: Cystatin C may be considered as an alternative and more accurate serum marker than serum creatinine or the Cockcroft and Gault estimated GFR in discriminating type 2 diabetic patients with reduced GFR from those with normal GFR.     

Renal scanning 99mTc diethylene-triamine pentaacetic acid glomerular filtration rate (GFR) determination compared with iothalamate clearance GFR in diabetics. The Collaborative Study Group for The study of Angiotensin-Converting Enzyme Inhibition in Diabetic Nephropathy.

Traditionally, creatinine clearance is used as an estimation of the glomerular filtration rate (GFR) because of its relative ease and low cost. Errors in collection limit its usefulness. Estimation of GFR using 99mTc diethylene-triamine pentaacetic acid (Tc-DTPA) by direct scintigraphic determination of fractional radionuclide accumulation within each kidney does not require blood or urine sampling, takes 10 to 15 minutes to perform, and has been reported to give a GFR that correlates with 24-hour urinary creatinine clearance (CC) in hospitalized patients (r = 0.95). To assess its usefulness in the outpatient diabetic with nephropathy, 24 patients with type I diabetes underwent 56 iothalamate clearances during water diuresis and 56 simultaneous Tc-DTPA GFR estimations. GFR was also estimated from 24-hour urinary CC, 100/creatinine, and by the formula of Cockcroft and Gault. Tc-DTPA GFR estimation by direct renal scanning correlated relatively poorly with iothalamate GFR (r = 0.74) in this patient population when all levels of iothalamate GFR were compared (n = 56), but improved (r = 0.80) when iothalamate GFR values greater than or equal to 120 mL/min were excluded from analysis (n = 45). Given all levels of iothalamate GFR, the best correlation was obtained with the estimation using the equation of Cockcroft and Gault (r = 0.86).     

Serum cystatin C as an endogenous marker of renal function in patients with chronic kidney disease

The estimation of the glomerular filtration rate (GFR) is an essential part of the evaluation of patients with chronic kidney disease (CKD). Recently, serum cystatin C has been proposed as a new endogenous marker of GFR. Authors compared serum creatinine, creatinine clearance calculated from Cockcroft and Gault formula and serum cystatin C against (51)CrEDTA clearance in 252 patients with CKD and GFR <90 mL/min/1.73 m(2). Analysis of correlations and diagnostic accuracy (receiver operating characteristic curves) of different GFR markers indicate that serum cystatin C is a more reliable marker of GFR in patients with CKD than serum creatinine.     

Serum creatinine can predict adequacy of peritoneal dialysis--preliminary report

AIM: To determine the value of creatinine clearance, estimated using the Cockcroft and Gault formula, in assessing adequacy of peritoneal dialysis. METHODS: We undertook a retrospective analysis of creatinine clearance results derived from a conventional 24-hour collection in 35 stable outpatients on peritoneal dialysis and compared them with those calculated from the corresponding serum creatinine using the Cockcroft and Gault formula. RESULTS: There was a strong correlation between the 2 methods (r = 0.82, p < 0.0001), although the formula tended to over-estimate clearances. The formula had a positive predictive value of 88% and a negative predictive value of 86% for detecting inadequate dialysis. CONCLUSION: The creatinine clearance calculated using the Cockcroft and Gault formula can be used in patients on peritoneal dialysis to estimate adequacy of dialysis. We believe that this method, which is far less expensive and time-consuming, deserves further testing in a larger population in order to define more accurately its role in the management of PD patients.     

An alternative formula to the Cockcroft-Gault and the modification of diet in renal diseases formulas in predicting GFR in individuals with type 1 diabetes

Chronic kidney disease is currently on the rise and not only leads to ESRD necessitating dialysis or transplantation but also increases cardiovascular disease risk. Measurement of the GFR, the gold standard for assessing kidney function, is expensive and cumbersome. Several prediction formulas that are based on serum creatinine are currently used to estimate the GFR, but none has been validated in a large cohort of individuals with diabetes. The performance of two commonly used formulas, the abbreviated Modification of Diet in Renal Disease (MDRD) study formula for the GFR and the Cockcroft-Gault estimate of creatinine clearance, were examined against GFR measured by the renal clearance of iothalamate in 1286 individuals with type 1 diabetes from the Diabetes Control and Complications Trial (DCCT). The performance of these formulas was assessed by computing bias, precision, and accuracy. The DCCT participants had normal serum creatinine, unlike the MDRD patients, and somewhat lower creatinine excretion than subjects in the original cohort Cockcroft Gault, which led to biased and highly variable estimates of GFR when these formulas were applied to the DCCT subjects. The MDRD substantially underestimated iothalamate GFR, whereas the Cockcroft Gault formula underestimated it when it was <120 ml/min per 1.73 m(2) and overestimated it when iothalamate GFR was >130 ml/min per 1.73 m(2). Overall, only one third of the formula's estimates were within +/-10% of iothalamate GFR. By underestimating GFR, these formulas were likely to flag early declines in kidney function. Refitting the MDRD formula to the DCCT data gave a more accurate and unbiased prediction of GFR from serum creatinine; percentage of estimate within 10% of measured GFR increased to 56%. A substantial variability in the estimates, however, remained.     

Creatinine clearance in the elderly: a comparison of direct measurement and calculation from serum creatinine

In 53 patients, aged over 70 years and admitted as urgent cases, creatinine clearance was determined biochemically in 24-hour urine and serum. The adjusted creatinine clearance value was compared with the values obtained by the formulas of Cockcroft and Gault [Nephron 16: 31-41, 1976], Kampmann et al. [Acta med. scand. 196: 517-520, 1974] and Hallynck et al. [Clin. Pharmacol. Ther. 30: 414-421, 1981] where creatinine clearance can be estimated from the serum creatinine concentration. A significant connection was found between the adjusted creatinine clearance and the values by the formula of Cockcroft and Gault (r = +0.46), compared with the formula of Kampmann et al. (r = +0.53), although only a small correlation was seen in comparison with the formula of Hallynck et al. (r = +0.30). A very high correlation of the obtained values was found by the formulas of Cockcroft and Gault and Kampmann et al. (r = +0.99) and also a significant correlation with the formula of Hallynck et al., (r = +0.56). By comparing the values according to formulas of Kampmann et al. and Hallynck et al. a significant connection was obtained (r = +0.59). The method of Cockcroft and Gault could be used as a fast analysis of creatinine clearance in older patients with great individual variation, as could the formula of Kampmann et al., but the determination of creatinine clearance by a biochemical method is a reliable reference.     

GFR prediction using the MDRD and Cockcroft and Gault equations in patients with end-stage renal disease.

BACKGROUND: Although prediction equations are recommended to determine GFR and creatinine clearance (CrCl), neither the MDRD equations nor the Cockcroft and Gault formula have been validated for the low levels of GFR present in end-stage renal disease (ESRD). The accuracy of the MDRD equations and the Cockcroft and Gault formula in predicting GFR and CrCl, respectively, was examined in patients with ESRD and its relationship to the basal GFR and two markers of malnutrition, urinary creatinine and body fat determined. METHODS: Inulin clearance (C(in)) was measured in 26 non-diabetic patients with ESRD and the 24 h CrCl determined. GFR was predicted using three equations derived from the MDRD study population containing four to six variables. Both CrCl and GFR were predicted from the Cockcroft and Gault formula. Estimates of bias and precision were obtained and Bland and Altman analysis performed. Body fat was measured by DEXA scan. RESULTS: The predicted GFR (MDRD) was 10% lower than C(in) (8.83+/-0.71 ml/min/1.73 m2) with all three MDRD equations, showing a similar degree of precision and bias. C(in) gave a negative correlation with the difference between the predicted GFR (MDRD) and the measured GFR. The predicted GFR (MDRD) underestimated GFR when C(in) >8 ml/min/1.73 m2 but overestimated GFR when C(in) <8 ml/min/1.73 m2. The Cockcroft and Gault formula overestimated CrCl by 14% and overestimated C(in) by 35%. C(in) gave a negative correlation with the difference between the predicted GFR (Cockcroft and Gault) and measured GFR, overestimating GFR when C(in) <13 ml/min/1.73 m2. The overestimation of GFR by the MDRD equation was not associated with urinary creatinine excretion. However, both Cockcroft and Gault and the MDRD predictions showed a positive, but weak, correlation with body fat. CONCLUSION: The MDRD equations were more accurate in predicting the group mean GFR in patients with ESRD than the Cockcroft and Gault formula. However, the predicted GFR using either formula was related to the basal GFR and percentage body fat.     

Inaccuracy of estimated creatinine clearance for prediction of iothalamate glomerular filtration rate

The clinical practice of estimating creatinine clearance (Ccr) from a patient's serum creatinine value by use of various nomograms and prediction formulas is widespread. The predictive accuracy of such Ccr estimates as substitutes for measured values of glomerular filtration rate (GFR) has not been determined. In addition, the effect of patient physical parameters on GFR prediction accuracy has not been assessed. To investigate these issues, 500 predicted Ccr values from each of four versions of the formula of Cockcroft and Gault were statistically compared with GFR values measured by sodium iothalamate clearance (Cio) in 394 human subjects representing every level of renal function. We conclude that (1) the original formula of Cockcroft and Gault is an inaccurate predictor of GFR; (2) correction of the formula for patient physical parameters does improve its accuracy for GFR prediction; (3) the best formula is not accurate enough to replace laboratory measurement of GFR; and (4) GFR prediction inaccuracy is more often associated with extremes in patient age, weight, serum creatinine, body surface area, and measured GFR but may occur for any value of each of these parameters.     

Kidney dimensions at sonography are correlated with glomerular filtration rate in renal transplant recipients and in kidney donors

The gold standard to assess renal function is the measurement of glomerular filtration rate (GFR). For practical reasons, renal function is often evaluated from serum creatinine (S Cr) or cystatin C (S Cys), and GFR is predicted from SCr. Ultrasound scanning of the kidneys is used only to evaluate renal morphology. The aim of this study was to evaluate the relationship between sonographic renal dimensions and GFR in renal transplant recipients and in kidney donors. GFR (urinary clearance of (99m)Tc-DTPA), S Cr, and S Cys were measured in 33 donors (28 females [F], 5 males [M]; SCr, 0.81-1.90 mg/dL) and 30 recipients (8 F, 22 M; SCr, 0.96-2.42 mg/dL). GFR was also predicted using the Cockcroft and Gault (CG) formula and with the simplified Modification of Diet in Renal Disease (MDRD) formula. Length, width, and depth of kidneys and renal sinus were measured using renal sonography. Among sonographic measurements, kidney length showed the best correlation with GFR. A closer correlation with GFR was found in donors (r = 0.639; P < .00007) than in recipients (r = 0.511; P < .005). In either case, the correlation of kidney length with GFR was greater than that of S Cr or S Cys, and similar to that of CG or MDRD GFR. Accuracy of kidney length as an indicator of GFR impairment was not statistically different from laboratory tests. Only in donors did CG show better accuracy. In conclusion, renal dimensions at sonography closely correlated with GFR. Thus, renal sonography can give information also on the function of the renal graft and of the remaining kidney of living donors.     

Serum creatinine as marker of kidney function in South Asians: a study of reduced GFR in adults in Pakistan

Migrant populations of South Asian origin have a higher risk for chronic kidney disease than the native whites. Several formulas have been developed to estimate kidney function from serum creatinine concentration. However, none of these has been validated in the South Asian population, which generally has different muscle mass composition than whites. A population-based cross-sectional study was performed on 262 individuals who were aged > or = 40 yr in Karachi, Pakistan. Reduced GFR was defined as creatinine clearance (Ccr) measured in 24-h urine collection of <60 ml/min per 1.73 m2. Creatinine excretion was compared with age- and gender-matched white individuals by comparison of observed versus expected results on the basis of a formula using t test. The agreement among Cockcroft Gault (CG) Ccr and Modification of Diet in Renal Disease (MDRD) Study GFR equations was assessed by regression analyses, and the degree of accuracy of estimated versus measured GFR was determined. Mean (95% confidence interval) creatinine excretion was 1.7 (1.0 to 2.4) mg/kg per d lower than expected for age- and gender-matched white individuals (P < 0.001). The coefficient of determination for measured Ccr on the logarithmic scale was 66.7 and 55.6% for the CG and MDRD Study equations, respectively. The proportion of estimates within 20, 30, and 50% of measured Ccr values was 47.7 versus 32.8% (P < 0.001), 64.9 versus 49.6% (P < 0.001), and 79.4 versus 72.9 (P = 0.07) for CG versus MDRD Study equations, respectively. Lower mean creatinine excretion in these individuals may explain, in part, suboptimal agreement between estimated versus measured GFR. Inclusion of terms for ethnic and racial groups other than white and black might improve the performance of GFR estimating equations.     

Estimated and Measured Donor Creatinine Clearance are Poor Predictors of Long-Term Renal Graft Function and Survival

The objective of this study was to evaluate estimated and measured donor renal function in predicting graft function long-term and to identify donor criteria associated with nonacceptable graft prognosis. In 200 consecutive cadaver donors creatinine clearance was measured at explantation and estimated using the Cockcroft formula on admission serum creatinine. Graft function was evaluated in recipients (n = 387) by 24-h creatinine clearance regularly during 3 years after transplantation. Measured creatinine clearance correlated to some extent with long-term graft function, while Cockcroft estimation was slightly superior and similar to using donor age only. Kidneys from donors with intra-operative creatinine clearance < or = 55 mL/min (median 50 mL/min) produced acceptable recipient graft function of 48 mL/min at 3 years and 76% 3-year graft survival. Donor age > or =60 years resulted in clearance at 3 years of 29 mL/min and 78% 3-year graft survival; adding the criteria of admission Cockcroft < or =60 mL/min, graft function at 3 years (28 mL/min) and 3-year graft survival (76%) were similar. In conclusion, creatinine-based estimates of the functional capacity of the donor kidney, calculated or intra-operatively measured, do little to improve the ability of donor age alone to predict long-term allograft function after renal transplantation, and nonacceptable donors are not discriminated.     

The estimation of glomerular filtration rate in an Australian and New Zealand cohort

Background: Accurate estimation of glomerular filtration rate (GFR) allows early detection of renal disease and maximizes opportunity for intervention. Aim: To assess the accuracy of estimated GFR (eGFR) in an Australian and New Zealand cohort with chronic kidney disease using the 4‐variable Modification of Diet in Renal Disease equation (MDRD_4V), the Chronic Kidney Disease Epidemiology Collaboration (CKD‐EPI) equations, and the Cockcroft and Gault equation with actual and ideal body weight. Methods: Retrospective review of patients who had measured GFR (mGFR) by 51Cr‐EDTA clearance and simultaneous measurements of serum biochemistry and anthropometrics. eGFR was compared with mGFR using the concordance correlation coefficient (CCC) and Bland–Altman measures of agreement. Results: 178 patients had 441 radioisotope measurements of GFR. Mean mGFR of was 22.6 mL/min per 1.73 m². The MDRD_4V equation using the ‘black’ correction factor was most accurate with a mean eGFR of 19.74 (CCC 0.733, bias ?2.86). The CKD‐EPI equations also using the ‘black’ correction factors were almost as good at 19.11 (CCC 0.719, bias ?3.49). The Cockcroft–Gault creatinine clearance values had the poorest agreement with mGFR. In the 18 nonwhite non‐Asian patients, the MDRD_4V and CKD‐EPI equations were generally less accurate although the use of the ‘black’ correction factor resulted in greater accuracy for both equations. Conclusion: The MDRD_4V equation was the most accurate. However, its accuracy might be less for nonwhite non‐Asian patients if the ‘black’ correction factor is omitted. Further study of the estimation of GFR in Australian and New Zealand ethnic subgroups would be helpful.     

Does cystatin C improve the precision of Cockcroft and Gault's creatinine clearance estimation?

BACKGROUND: Cystatin C is increasingly used to estimate renal function, but its large intraindividual variability limits its practical value. This study aimed at verifying whether the clinical practice of associating cystatin C determination with serum creatinine (Cr) improved the ability of the Cockcroft and Gault formula to estimate creatinine clearance (CrCl). METHODS: It was an observational cross-sectional study of 134 in-patients with mildly impaired renal function. Using the Hoek et al formula (glomerular filtration rate (GFR)/1.73m2 = - 4.32 + 80.35/cystatin C mg/L), multivariate linear regressions (LREG) and artificial neural networks (ANN), we integrated cystatin C in the Cockcroft and Gault formula and analyzed the potential superiority of this procedure by comparing its performance with that of the two algorithms taken separately. RESULTS: The inclusion of cystatin C in the Cockcroft and Gault formula using the data of an LREG (CrCl = 0.371 x (Hoek et al) + 0.589 x Cockcroft and Gault), a simple mean between the two algorithms or ANN ameliorated the CrCl estimation precision allowing an absolute error reduction of approximately 4, 4 and 6%, respectively (relative values 12, 12 and 17%). CONCLUSIONS: Although the combination of the Hoek et al and Cockcroft and Gault formulae using both linear and non-linear mathematical methods allowed a statistically significant reduction in the estimation error generated by Cockcroft and Gault, considering the small impact on the estimation precision and the large intraindividual variation of both cystatin C and Cr, this procedure probably has no clinical relevance.     

Evaluation and applicability of predictive equations of the glomerular filtration rate in chronic kidney disease

Prediction equations of glomerular filtration rate (GFR) may facilitate early detection, evaluation and management of chronic kidney disease (CKD). However, the reliability of these equations was not extensively studied in our CKD population. Hence, the present study was aimed to determine the performance of modification of diet in renal disease (MDRD) and Cock-croft Gault formulas in predicting GFR in CKD patients and their relationship with the measured GFR. A total of 104 subjects (71 male and 33 female, aged 26-68 years) with different stages of CKD were recruited for this study; we excluded 51 patients due to improper collection of 24-h urine. The GFR was measured using 24-h creatinine clearance and predicted by the Cockcroft Gault, the 4-variable MDRD and the 6-variable MDRD equations. Prediction equations correlated well with the measured GFR. However, the predicted GFR using the 4-variable MDRD equation revealed a highly significant positive correlation with the GFR measured by creatinine clearance (r = 0.86, P < 0.001), followed by the 6-variable MDRD and Cockcroft-Gault equations with r = 0.85 and 0.77, P < 0.001, respectively. In conclusion, the present study predicts that the 4-variable MDRD is the best available equation for predicting GFR in our CKD population.     

不同公式估算慢性肾脏病患者肾小球滤过率的结果评价

目的探讨不同估算公式估算慢性肾脏病（CKD）患者肾小球滤过率（GFR）在肾功能评价中的价值。方法选择CKD患者239例,所有患者同步检测99锝-二乙烯三胺五乙酸（^99mTc-DTPA）、GFR、血肌酐（SCr）等。将^99mTc-DTPA测定的GFR作为参照,并用肾脏病膳食改良试验（MDRD）公式、Cockcroft-Gault公式、简化MDRD公式及慢性肾脏病流行病合作研究（cKD-EPI）公式计算估测GFR,比较不同CKD分期中各估算公式估算的GFR的准确性。结果各估算公式估算的GFR值均高于^99mTc-DTPA,MDRD公式偏离程度最大;各估算公式估算的GFR值与^99mTc-DTPA检查的GFR结果有相关性,CKD-EPI公式相关性最高。结论CKD-EPI公式估算肾功能更接近^99mTc-DTPA的结果,但仍需进一步校正。     

Measurement of glomerular filtration rate in renal transplant recipients: A comparison of methods

SUMMARY: While single injection radionuclide and radio‐contrast glomerular filtration rate (GFR) clearance methods are widely used, the relative accuracy of single versus multiple sample techniques continues to be debated. In addition, GFR calculated from the serum creatinine concentration is considered by some to produce results comparable to clearance methods. In this study, 109 patients with stable renal transplant fraction were prospectively evaluated by yearly ⁵¹Cr EDTA clearance as well as by three published formulae used to predict GFR from serum creatinine. Analysis of 362 measurements demonstrated a highly significant correlation between multiple and single point clearance results, as well as the serum creatinine nomograms using least squares regression analysis (P<0.001). the mean GFR was, however, significantly higher using the Cockcroft and Gault formula; 64 ± 18 compared with 47 ± 14 and 50 ± 14 with other serum creatinine formulae, and 46 ± 21–50 ± 17mL/min per 1.73m2 with the three ⁵¹Cr EDTA methods (P<0.01). However, further statistical analysis using more appropriate methods, including an analysis of difference and least product regression analysis did not support any of the methods tested as reliable alternatives to multiple sample ⁵¹Cr EDTA clearance, because both fixed and proportional bias was noted. In a subgroup of 29 patients evaluated yearly over the 7‐year study period, serum creatinine derivations all demonstrated a greater year to year mean fluctuation compared with clearance methods. It is oncluded that while each GFR method has similarities, they are not interchangeable. Until clearance methods and serum creatinine formulae are directly compared with inulin clearance with the use of appropriate statistical evaluation, it is recommended that the Chantler 3 sample ⁵¹Cr EDTA method be the method of choice in clinical laboratories.     

Renal volume assessed by magnetic resonance imaging volumetry correlates with renal function in living kidney donors pre‐ and postdonation: a retrospective cohort study

Renal function of potential living kidney donors is routinely assessed with scintigraphy. Kidney anatomy is evaluated by imaging techniques such as magnetic resonance imaging (MRI). We evaluated if a MRI‐based renal volumetry is a good predictor of kidney function pre‐ and postdonation. We retrospectively analyzed the renal volume (RV) in a MRI of 100 living kidney donors. RV was correlated with the tubular excretion rate (TER) of MAG3‐scintigraphy, a measured creatinine clearance (CrCl), and the estimated glomerular filtration rate (eGFR) by Cockcroft‐Gault (CG), CKD‐EPI, and modification of diet in renal disease (MDRD) formula pre‐ and postdonation during a follow‐up of 3 years. RV correlated significantly with the TER (total: r = 0.6735, P < 0.0001). Correlation between RV and renal function was the highest for eGFR by CG (r = 0.5595, P < 0.0001), in comparison with CrCl, MDRD‐GFR, and CKD‐EPI‐GFR predonation. RV significantly correlated with CG‐GFR postdonation and predicted CG‐GFR until 3 years after donation. MRI renal volumetry might be an alternative technique for the evaluation of split renal function and prediction of renal function postdonation in living kidney donors.     

Estimation of the glomerular filtration rate through different methods in kidney transplant recipients: correlation with the creatinine clearance measurement

The measurement of the glomerular filtration rate (GFR) is an important tool for physicians to follow kidney transplant recipients. Indeed, renal function has been shown to be predictive of graft outcome in retrospective studies. Several methods have been proposed to measure GFR. In the present study we evaluated the correlation of GFR between a reference method (calculation through the urine to plasma ratio of creatinine [UV/P] formula) and three estimation equations (Cockcroft and Gault; Nankivell; modification of diet in renal disease) in 81 kidney transplant recipients at 3 and 12 months posttransplantation. We showed a significant correlation between the three predictive formulas and UV/P, but none of the predictive equations showed an excellent correlation. The best correlation between an estimation equation and the UV/P formula was the CG formula. Further studies are required to compare the estimated GFR with better reference methods, such as the use of isotopic markers in kidney graft recipients.     

Importance of creatinine clearance for drug dosing in nursing home residents

Serum creatinine is often not an adequate measure of renal function, especially in advanced age or in physically debilitated patients. Estimated creatinine clearance is necessary to decide on usage of drugs such as Metformin. This study included 64 nursing home residents with diabetes treated with Metformin. Creatinine clearance (CrCl) was calculated by the Cockcroft–Gault equation modified for ideal body weight. CrCl more than or equal to 60/mL min was used as a cut-off for appropriate use of Metformin. In our sample, 20.3% had renal failure when measured by serum creatinine while 56.3% had renal failure when measured by CrCl. Age >65 years and women were more likely to be classified as normal for serum creatinine but have abnormal creatinine clearance. Use of estimated creatinine clearance should be advocated instead of serum creatinine when prescribing Metformin, especially for those of older age and among women.     

A simple method for correcting overestimated glomerular filtration rate in obese subjects evaluated by the Cockcroft and Gault formula: a comparison with 51Cr EDTA clearance

AIM: The Cockcroft and Gault formula is a quick and reliable method for calculating creatinine clearance without a 24-hour urine collection (CG-cl). In obese subjects an excess of fat mass provokes a reduction in daily creatinine urine excretion per body kilo weight and is responsible for overestimated renal function when calculated by CG-cl. The aim of this study was to devise a simple correction method which could also make use of CG-cl in obese subjects. PATIENTS AND METHODS: In 52 subjects with a body mass index (BMI) > 25, renal function was assessed by simultaneously determining creatinine clearance using 24-hour urine collection (Cr-cl) and the CG-cl. The percentage difference between the 2 clearances (delta %) was correlated with BMI for each patient using simple linear regression analysis. The estimated regression model (delta% = 1.217 BMI-- 24.81) provided the following CG-cl correction formula for obese subjects: Corrected CG-cl = CG-cl (1.25 - 0.012 BMI). Its validity was evaluated in another group of 20 subjects with BMI > 25 by comparing the results obtained with Corrected CG-cl to those obtained by CG-cl and MDRD formula (MDRD-cl) using the clearance of 51Cr-EDTA (5 Cr-EDTA-cl) as the GFR measurement gold standard. RESULTS AND CONCLUSION: Linear regression analysis of CG-cl, MDRD-cl and Corrected CG-cl compared to 5tCr-EDTA-cl (considered as the independent variable) resulted in the following determination coefficients (R2): 0.687; 0.818; 0.947, respectively. In conclusion, this formula can be considered a quick and reliable method for CG-cl correction in obese subjects.