Cystatin C-based Glomerular Filtration Rate Research Articles

Cystatin C-estimated Glomerular Filtration Rate in Pediatric Autologous Hematopoietic Stem Cell Transplantation

Formal evaluation of kidney function is essential to determine chemotherapy dosing based on established treatment protocols in children undergoing autologous stem cell transplantation. Cystatin C has been widely studied as a marker of the glomerular filtration rate (GFR), although data regarding its use in stem cell transplantation are limited. We evaluated the performance of cystatin C-based equations and determined their sensitivity to detect a nuclear GFR of <100 mL/min/1.73 m(2) in children undergoing autologous transplantation. We performed a retrospective cohort analysis in 16 children undergoing 26 transplantations using a modified Bland-Altman analysis to account for repeated measures. Cystatin C-based equations published by Hoek, Le Bricon, Rule, Filler, Zappitelli, Larsson, and Schwartz (the New Chronic Kidney Disease in Children formula, New CKiD formula) were evaluated and compared to the creatinine-based modified Schwartz equation. We found that cystatin C-based equations demonstrated improved sensitivity to detect a nuclear GFR of <100 mL/min/1.73 m(2) compared to the creatinine-based modified Schwartz equation, which significantly overestimated GFR. Most cystatin C-based equations, however, tended to underestimate the nuclear GFR. The New CKiD formula, combining cystatin C and creatinine, offered a sensitivity of 100% and a specificity of 95% for detecting a nuclear GFR <100 mL/min/1.73 m(2). Institutions using cystatin C-based GFR estimation should be aware of the specific prediction formula and GFR measurement techniques available at their center, as each method's performance can vary considerably. As more research becomes available, this easily measured marker should become a valuable component of GFR estimation, providing cost savings (a nuclear GFR is 5.5 times more costly than a cystatin C) and reducing radiation exposure.

Is the Chronic Kidney Disease Epidemiology Collaboration four‐level race equation better than the cystatin C equation?

To evaluate the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) four-level race equation in the assessment of glomerular filtration rate (GFR) in Chinese people with chronic kidney disease (CKD), which was published in 2011, compared with the cystatin C-based GFR estimation equation (CysC GFR) and the combination of CysC and serum creatinine equation (CysC-Scr GFR). The CKD-EPI four-level race equation estimated GFR (CKD-EPI GFR) was compared with the CysC GFR and CysC-Scr GFR. Three equations were compared with body surface area (BSA) standardized GFR (sGFR), which was measured by (99m) Tc-DTPA renal dynamic imaging method in 111 CKD cases. A statistically significant correlation was found between sGFR and CKD-EPI GFR, CysC GFR and CysC-Scr GFR. Three estimated GFR (eGFR) equations of 30% accuracy were 58.6%, 56.8% and 63.5%, respectively. Average deviations of eGFR from sGFR were 2.34, 1.19, and 1.32 (mL/min per 1.73 m(2)) (P > 0.05), respectively. There was no significant deviation in the CKD from stages 1 to 5 in CKD-EPI GFR and CysC-Scr GFR. However, when estimated by CysC GFR, the deviation was increased, with the value of 12.41 mL/min per 1.73 m(2) (P= 0.002) in CKD stage 5. Our results showed that in a Chinese population with CKD, CKD-EPI GFR, CysC GFR and CysC-Scr GFR of bias and overall accuracy of 30% were very similar. There was little advantage in adding Asian coefficient to modifying the CKD-EPI equation. CysC GFR overestimated GFR in patients with CKD stages 4 and 5.

Cystatin C is not a good candidate biomarker for HNF1A-MODY

Cystatin C is a marker of glomerular filtration rate (GFR). Its level is influenced, among the others, by CRP whose concentration is decreased in HNF1A-MODY. We hypothesized that cystatin C level might be altered in HNF1A-MODY. We aimed to evaluate cystatin C in HNF1A-MODY both as a diagnostic marker and as a method of assessing GFR. We initially examined 51 HNF1A-MODY patients, 56 subjects with type 1 diabetes (T1DM), 39 with type 2 diabetes (T2DM) and 43 non-diabetic individuals (ND) from Poland. Subjects from two UK centres were used as replication panels: including 215 HNF1A-MODY, 203 T2DM, 39 HNF4A-MODY, 170 GCK-MODY, 17 HNF1B-MODY and 58 T1DM patients. The data were analysed with additive models, adjusting for gender, age, BMI and estimated GFR (creatinine). In the Polish subjects, adjusted cystatin C level in HNF1A-MODY was lower compared with T1DM, T2DM and ND (p < 0.05). Additionally, cystatin C-based GFR was higher than that calculated from creatinine level (p < 0.0001) in HNF1A-MODY, while the two GFR estimates were similar or cystatin C-based lower in the other groups. In the UK subjects, there were no differences in cystatin C between HNF1A-MODY and the other diabetic subgroups, except HNF1B-MODY. In UK HNF1A-MODY, cystatin C-based GFR estimate was higher than the creatinine-based one (p < 0.0001). Concluding, we could not confirm our hypothesis (supported by the Polish results) that cystatin C level is altered by HNF1A mutations; thus, it cannot be used as a biomarker for HNF1A-MODY. In HNF1A-MODY, the cystatin C-based GFR estimate is higher than the creatinine-based one.

Cystatin C – A Fast and Reliable Biomarker for Glomerular Filtration Rate in Head and Neck Cancer Patients

Determination of renal function is a prerequisite for planning therapy in cancer patients. Limitations of creatinine as marker for the glomerular filtration rate (GFR) led to the proposal of cystatin C as a more accurate biomarker especially in mild renal insufficiency or in patients with low muscle mass. We compared the accuracy of cystatin C- and creatinine-based equations to estimate GFR in head and neck cancer (HNC) patients receiving platinum-based radiochemotherapy. The study population consisted of 52 HNC patients (GFR range, 37-105 mL/min/1.73 m(2) complemented by 17 patients with known renal insufficiency (GFR range, 10-60 mL/min/1.73 m(2)). Intraclass correlation coefficients were calculated between the reference method (51)Cr-EDTA clearance and estimated GFR by creatinine clearance and equations based on creatinine (Cockroft-Gault, modification of diet in renal disease (MDRD), Wright) or cystatin C (Larsson, Dade-Behring, Hoek). In addition, sensitivity and specificity to discriminate GFR > 60 mL/min/1.73 m(2) were evaluated by receiver operating characteristic curve (ROC). The highest correlation coefficients were found for the cystatin C-based estimates in comparison with creatinine-based estimates or creatinine clearance, even though Bland-Altman plots revealed GFR overestimation for all equations tested. The cystatin C-based Hoek formula exhibited the highest overall precision and accuracy. GFR of < 60 mL/min/1.73 m(2) was assumed as a cut-off for chemotherapy. ROC analyses revealed the highest AUC to predict a GFR > 60 mL/min/1.73 m(2) for the creatinine-based Wright formula, closely followed by the MDRD formula and cystatin C-based equations of Larsson, Dade-Behring, and Hoek. Cystatin C-based GFR estimates showed the overall strongest correlation to the reference method. Thus, we recommend cystatin C for GFR estimation in HNC patients as an alternative method to the estimated creatinine clearance in clinical practice.

Performance of the creatinine-based and the cystatin C-based glomerular filtration rate (GFR) estimating equations in a heterogenous sample of patients referred for nuclear GFR testing

Cystatin C may be a more accurate marker of the glomerular filtration rate (GFR) than creatinine. We evaluated the performance of the creatinine-based abbreviated modification of diet in renal disease (MDRD), the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations, and 6 cystatin C-based equations in estimating GFR (eGFR) in a heterogeneous sample of patients. Measured GFR (mGFR) was obtained from the plasma clearance of 99mtechnetium Diethylenetriaminepentaacetic acid in 42 adult patients referred for nuclear GFR testing (January to March 2008). We evaluated the bias, precision, and accuracy of the abbreviated MDRD, CKD-EPI, Filler, Grubb, Hoek, Larsson, Le Bricon, and Rule eGFR equations. Participants had a mean mGFR of 70.9 mL/min/1.73 m2 (range: 22-125 mL/min/1.73 m2), a median age of 57 years (interquartile range: 45, 66), were 62% male, and were 38% liver transplant recipients. Correlation coefficients between eGFRs and mGFR ranged from 0.65 to 0.87 (each P<0.001). The cystatin C-based Hoek equation had the best overall performance with a low bias (-1.4 mL/min/1.73 m2), good precision (13.3 mL/min/1.73 m2), and greatest accuracy, with 93% of values within 30% of mGFR. Although the CKD-EPI equation had the lowest bias (-0.6 mL/min/1.73 m2), it had poor precision (20.7 mL/min/1.73 m2) and low accuracy, with only 69% of values within 30% of mGFR. The Hoek equation remained accurate and had the least bias when patients were grouped according to the history of liver transplantation and the mGFR above or below 60 mL/min/1.73 m2. In this heterogeneous sample, the cystatin C-based Hoek equation performed the best overall, regardless of mGFR level or history of liver transplantation.

Cystatin C in Diabetics as a Marker of Mild Renal Insufficiency after CABG

The purpose of this study was to evaluate the accuracy of plasma cystatin C in acute impairment in renal function; plasma cystatin C was compared to plasma creatinine in two hundred patients undergoing elective CABG surgery. We performed a prospective clinical study of two hundred patients undergoing coronary bypass surgery. Plasma creatinine and cystatin C were measured preoperatively and on the first and fourth days after surgery. Estimated glomerular filtration rate (GFR) was calculated using one creatinine-based and two cystatin C-based equations. There were 144 non-diabetic and 56 diabetic patients. The need for furosemide was more common among diabetics (80.4% of the patients vs. 53.9%, p = 0.024). Changes in cystatin C-based GFR with both equations were significantly greater in the group of diabetics (-14.3 ± 28.0 and -11.2 ± 19.3 ml/min/1.73 m(2) vs. -4.3 ± 26.9 and -3.1 ± 20.5 ml/min/1.73 m(2), p = 0.025 and 0.016, respectively). Changes in creatinine-based GFR did not differ between the diabetics and the non-diabetics. Cystatin C and cystatin C-based estimation of GFR may be useful and more sensitive than creatinine in detecting mild acute renal insufficiency in diabetic patients.

Cystatin C in acute kidney injury

This review will summarize and discuss the role of cystatin C in the diagnosis of acute kidney injury. Cystatin C is easily measured and has the characteristics of an ideal marker of kidney function. Data suggest that cystatin C is modified by age, sex, muscle mass, obesity, smoking status, thyroid function, inflammation, and malignancy. These factors suggest the need for age-specific and sex-specific reference standards. Cystatin C-based glomerular filtration rate estimates may perform better than creatinine in selected patient populations (elderly, children, transplantation, cirrhosis, malnourished). Cystatin C has been evaluated for the early diagnosis of acute kidney injury (AKI) in several populations. Serum cystatin C has value for the diagnosis of acute kidney injury; however, it has often performed similarly to creatinine. Urinary cystatin C has potential as an early marker. Cystatin C is an accurate biomarker for the early detection of AKI, and may, in selected populations, be superior to creatinine; however, data have been inconsistent. It also has reasonable discrimination for important outcomes such as death and renal replacement therapy (RRT). Additional studies are needed that focus on the cost-effectiveness of earlier detection of AKI with cystatin C compared with creatinine, and whether these biomarkers have complementary value.

Use of cystatin C as a biomarker for glomerular filtration rate in patients with head and neck cancer receiving cisplatin-based chemotherapy.

5592 Background: Determination of renal function is a prerequisite for planning therapy in cancer patients. Limitations of creatinine as marker for the glomerular filtration rate (GFR) led to the proposal of cystatin C as a more accurate biomarker especially in mild renal insufficiency or in patients with low muscle mass. We compared the accuracy of cystatin C- and creatinine-based equations to estimate GFR in patients with head and neck cancer (HNC) receiving platinum based chemotherapy. Methods: The study population consisted of 50 HNC patients (GFR range 37-105 mL/min/1.73 m2), complemented by 19 patients with known renal insufficiency (GFR range 10-60 mL/min/1.73 m2). Intra-class correlation coefficients were calculated between the reference method (51)Cr-EDTA clearance and estimated GFR by creatinine clearance and equations based on creatinine (Cockroft-Gault, Modified-Diet-in-Renal-Disease, Wright) or cystatin C (Larsson, Dade- Behring, Hoek). Additionally, sensitivity and specificity to discriminate GFR < 60 mL/min/1.73 m2 were evaluated by receiver-operating- characteristic-curve (ROC). Results: The highest correlation coefficients were found for the cystatin C-based estimates in comparison with creatinine-based estimates or creatinine clearance, even though Bland-Altman plots revealed GFR overestimation for all equations tested. The cystatin C-based Hoek formula exhibited the highest overall precision and accuracy. GFR of > 60 mL/min/1.73 m2 was assumed as cut-off for chemotherapy, ROC analyses revealed the highest AUC for the creatinine-based Wright formula, closely followed by modified diet in renal disease formula and cystatin C-based equations of Larsson, Dade-Behring and Hoek. Conclusions: Cystatin C-based GFR estimates showed the over-all strongest correlation to the reference method. Thus, we recommend cystatin C for GFR estimation in HNC patients as alternative method to the estimated creatinine clearance in clinical practice to avoid nephrotoxicity in patients receiving platinum based chemotherapy. No significant financial relationships to disclose.

Mild renal dysfunction as a non-traditional cardiovascular risk factor?—Association of cystatin C-based glomerular filtration rate with flow-mediated vasodilation

Objective Chronic kidney disease, at least in its advanced stages, can be regarded as a non-traditional cardiovascular risk factor. The purpose of this study was to evaluate whether early stages of renal dysfunction are associated with flow-mediated vasodilatation, as an early marker of the atherosclerotic disease process. Methods In 1515 subjects (753 females) from the population-based Study of Health in Pomerania, the relationship between flow-mediated vasodilatation of the brachial artery (cuff occlusion of the forearm for 5 min) and glomerular filtration rate, estimated on the basis of serum cystatin C levels, was analyzed under consideration of various cardiovascular risk factors. Results Flow-mediated vasodilatation was 5.75 ± 0.16% in women and 4.29 ± 0.12% in men (mean ± SEM). Glomerular filtration rate amounted to 94.2 ± 0.7 ml/min/1.73 m 2, with 8.1% subjects with glomerular filtration rate ≤ 60 ml/min/1.73 m 2. Flow-mediated vasodilatation significantly correlated with glomerular filtration rate in the entire population ( r = 0.237, p < 0.001), in women ( r = 0.224, p < 0.001) and in men ( r = 0.168, p < 0.001). Adjusting for age and multiple cardiovascular risk factors and also for high-sensitive C-reactive protein levels revealed a significant association of flow-mediated vasodilatation and glomerular filtration rate in women ( p = 0.01), but not in men, with similar results when the analyses were restricted to individuals with glomerular filtration rate >60 ml/min/1.73 m 2. Conclusion Mild reduction in renal function is associated with alterations in endothelial function in females. Hence, very mild alterations in kidney function may also be regarded as a cardiovascular risk factor at least in women.

Monitoring renal function in children with Fabry disease: comparisons of measured and creatinine-based estimated glomerular filtration rate

Studies on renal function in children with Fabry disease have mainly been done using estimated creatinine-based glomerular filtration rate (GFR). The aim of this study was to compare estimated creatinine-based GFR (eGFR) with measured GFR (mGFR) in children with Fabry disease and normal renal function. Eighty-two examinations were done in 42 children (24 boys, 18 girls) with Fabry disease from three different centres. The mean age was 12.3 years. GFR was measured with iohexol, Cr(51)-EDTA or iothalamate, and the mean mGFR was 108 ml/min/1.73 m(2). The widely used original Schwartz formula (1976) overestimated GFR substantially by 50.6 ml/min/1.73 m(2) with a very low accuracy, whereas the new abbreviated Schwartz formula (2009) showed relatively good performances with a mean GFR overestimation of 5.3 ml/min/1.73 m(2) and 79% of the eGFR calculated within 20% of mGFR, thus being only slightly superior to the Counahan-Barratt formula. However, less than half of the eGFR calculated by the new abbreviated Schwartz equation were within 10% of the mGFR. When repeated measurements were performed, mGFR showed less variation than eGFR. The new abbreviated Schwartz formula should replace the original Schwartz formula in the routine follow-up of children with Fabry disease. The current creatinine-based GFR formulas are all hampered by low accuracy in the 'creatinine-blind' GFR range, and early progressive disease may be missed. Supplemental mGFR is, therefore, recommended in patients where changes in GFR have potential impact on important treatment regimens. Cystatin C-based GFR formulas remain to be validated in Fabry children.

Performance evaluation of a particle-enhanced turbidimetric cystatin C assay using the Abbott Aeroset analyser and assessment of cystatin C-based equations for estimating glomerular filtration rate in chronic kidney disease

Measurement of glomerular filtration rate (GFR) is critical for the diagnosis and stratification of chronic kidney disease (CKD). Recent studies have shown that cystatin C is superior to creatinine for the detection of impaired GFR, and several cystatin C-based equations for estimating GFR have been developed for this clinical application. We conducted the present study to assess the applicability of cystatin C as a routine clinical laboratory index and to determine the performance of cystatin C-based equations in estimating GFR in CKD patients in China. Performance evaluation of particle-enhanced turbidimetric cystatin C assay on the Abbott Aeroset analyser was carried out according to the National Committee for Clinical Laboratory document EP10-A2. Estimated GFR, which was generated from cystatin C-based equations, was compared with measured GFR, which was detected by plasma clearance of 99mTc-DTPA. Our cystatin C assay showed a very low total imprecision and linearity drift. All eight cystatin C-based GFR estimating equations underestimated or overestimated GFR as compared with GFR determined by 99mTc-DTPA clearance. Although the cystatin C assay is acceptable for routine clinical laboratory monitoring, none of the existing cystatin C-based equations were ideal for estimating GFR in Chinese CKD patients.

Validation of a new plasma cystatin C-based formula and the Modification of Diet in Renal Disease creatinine-based formula for determination of glomerular filtration rate

New proposed definitions of chronic kidney disease necessitate the development and use of simple and accurate methods for estimating glomerular filtration rate (GFR). Plasma cystatin C has been shown to be a more reliable GFR marker than creatinine and formulae for estimating GFR have been reported. The purpose of this study was to validate a cystatin C-based GFR prediction equation in a different population from the derivation set but using the cystatin C assay of a single laboratory, and to compare the results with that of the creatinine-based Modification of Diet in Renal Disease (MDRD) Study equation. A newly presented formula based on plasma cystatin C and gender and the MDRD formula based on creatinine for estimation of GFR were validated in an unselective patient material. Single sample iohexol clearance was used as the GFR reference method in 406 consecutive patients with GFR varying from normal to poor renal function. The creatinine assay used was standardized to express true plasma creatinine. Median bias (1.1%) and accuracy (79.1% of the estimates within +/-30% of iohexol clearance) of the cystatin C formula were close to the derivation set. The accuracy was significantly higher than that of the original four-variable MDRD equation (73.2%; median bias 9.8%). However, the accuracy did not differ significantly from that of the re-expressed MDRD formula (79.6%; median bias 3.2%) based on true creatinine. Both formulae performed with a low bias and acceptable accuracy up to a GFR of 90 ml/min/1.73 m(2). GFR estimation based on plasma cystatin C performed equally well in the validation as in the derivation set, and was as accurate as the re-expressed MDRD creatinine-based equation.

Comparative study of cystatin C and serum creatinine in the estimative of glomerular filtration rate in children

BackgroundTo compare estimated glomerular filtration rate (GFR) by Schwartz formula and cystatin C-derived formula in a large population of children with a large spectrum of renal disease. MethodsSerum creatinine, cystatin C and estimated GFR were determined in 273 children, 254 with renal disease, and a mean age of 10.0±4.4 y. Nineteen children were used as control, with a mean age of 8.5±4.2 y. ResultsThe children had nephrotic syndrome (16.5%), glomerulonephritis (11.4%), neurogenic bladder (11.4%), hydronephrosis (9.8%), asymptomatic hematuria (11%), chronic renal disease (5.9%) and other diseases (11%). Cystatin C, creatinine, Schwartz estimated GFR and cystatin C estimated GFR (mean±SD) were 1.30±1.03 mg/dl, 0.82±1.20 mg/l, 143±72 ml/min/1.73 m2 and 88±36 ml/min/1.73 m2, respectively. Although GFR estimated by creatinine and cystatin C had a significant correlation, the Bland–Altman analysis showed greater differences between GFR estimated by the 2 methods, with a mean difference of 50 ml/min. Besides, >50% of the patients with a reduced cystatin C estimated GFR had a normal GFR when analyzed by the Schwartz formula. ConclusionsOur data shows that cystatin C-based GFR is more sensitive than previous study had demonstrated. It is important to perform studies in specific populations to determine the variability in GFR measurements.

Comparison between creatinine and cystatin C-based GFR equations in renal transplantation

Estimation of glomerular filtration rate (GFR) from serum creatinine (Scr) or cystatin C (Cys C) exhibit variable performances. We compared the performances of 14 Scr and 9 Cys C estimated GFR equations using inulin clearance (Clin) as the reference test in 103 stable renal transplant populations. Bias, precision, receiving operation characteristics (ROC), accuracy within 30% ranges from the reference method and agreements of each test were compared. Mean Clin was 46.4+/-20.9 ml/min/1.73 m2. Scr and Cys C levels correlated well with each other (r=0.83, P<0.0001) and with Clin (r=-0.57 and -0.53, P<0.001, respectively). ROC analysis demonstrated no superiority of Cys C over Scr. Gats equation achieved the highest accuracy of 70% in patients with GFR>or=60 ml/min/1.73 m2. In patients with GFR>or=60 ml/min/1.73 m2, the Nankivell equation demonstrated the highest accuracy of 73.91%. Cys C-based equations were not depicted to be thoroughly accurate. Bias, precision and agreement were otherwise similar in all GFR tests. Scr-based equations did not appear to be inferior to Cys C-based equations as a means to estimate GFR in renal transplant patients.

Assessment of the Accuracy and Precision of Cystatin C-based GFR Estimates and Cr-based GFR Estimates in Comparison with Cr51-EDTA GFR

Cystatin C (cysC) is said to be an ideal marker for glomerular filtration rate (GFR), independent of external factors such as age, nutrition and inflammation. The authors compared the accuracy and precision of cysC-based and creatinine (Cr)-based GFR estimates using Cr51-EDTA GFR method as a reference. Serum concentrations of cysC and Cr were measured in adults over 17 yr (n=170) and children below 17 yr (n=79) who had had GFR estimated by Cr51-EDTA method. CysC-based GFR was estimated by the formula of Thierry [CysC-based GFR estimates (mL/min/1.73 m2)=78 x (1/cysC, in mg/L)+4] and Cr-based GFR by the formula of modified Modification of Diet in Renal Disease [MDRD II, Cr-based GFR estimates (mL/min/1.73 m2)=186 x (Scr)(-1.154) x (Age)(-0.203) x 0.742 (for a female patient) x 1.212 (for a black patient). In comparison with Cr51-EDTA GFR, in children below 17 yr, the bias +/- standard deviation (SD) of cysC-based and Cr-based GFR estimates were 7.5 +/- 6.1 and 106.5 +/- 98.2, respectively, in the range of below 90 of Cr51-EDTA GFR (mL/min/1.73 m2), and 33.7 +/- 33.0 and 174.4 +/- 18.8 in the range of over 90. In adults over 17 yr, the respective figures were 13.1 +/- 11.0 and 17.4 +/- 29.8 in below 90, and 21.2 +/- 20.1 and 83.6 +/- 108.8 in over 90 of Cr51-EDTA GFR. CysC-based GFR estimates show acceptable ranges of biases over the whole age and GFR ranges. CysC-based GFR estimates is considered to be the marker for GFR, which could be used without limitation of age and GFR ranges.

The Cockcroft-Gault formula should not be used in children

Although designed for adults, the Cockcroft-Gault formula was recently proposed for use in children > or =13 years of age. We compared the feasibility of the Cockcroft-Gault formula against the standard pediatric Schwartz formula and a novel cystatin C-based formula. Our patient cohort included 262 children aged 1 to 18 years with various renal pathologies, who underwent a 99-technetium diethylenetriaminepentaacetate ((99)Tc DTPA) glomerular filtration rate (GFR) renal scan. Calculations were performed in Systeme International (SI) units using published constants and recalculated constants from our patient population. Agreement was assessed using Bland and Altman analysis. Published and recalculated constants for the Cockcroft-Gault formula were 1.23 and 0.96, respectively, for boys, and 1.05 and 0.90, respectively, for girls. The published and recalculated constants for the Schwartz formula were 48 and 49.9, respectively, for boys > or =13 years old, and 38 and 46.2, respectively, for all girls and for boys <13 years old. Using published constants, there was agreement between GFR and Cockcroft-Gault formula in boys > or =13 years old (average bias 5.0 +/- 23.5%) while there was an average error of -19.0%+/- 36.4% for all ages. Similarly, the average bias with Schwartz for boys > or =13 years old was -6.8 +/- 24.0% and for all patients was -12.8 +/- 24.2%. Using recalculated constants, the average bias with Cockcroft-Gault in boys > or =13 years old was -19.8 +/- 23.5% and for all patients was -38.5 +/- 35.2%. Similarly, the average bias with Schwartz for boys < or =13 years old was -1.1 +/- 24.3% and for all patients was 3.0 +/- 24.0%. The novel cystatin C-based GFR calculations showed an average error of -4.9 +/- 20.3% in the adolescent boys and 2.4 +/- 20.4% for all ages. Cockcroft-Gault formula showed the worst agreement with GFR, regardless of using published or recalculated constants. The cystatin C-based approach resulted in the least error, and should be used for estimation of GFR.