Estimation of GFR using ß-trace protein in children.

BACKGROUND AND OBJECTIVES: Sex may affect the performance of small molecular weight proteins as markers of GFR because of differences in fat mass between the two sexes. The hypothesis was that the diagnostic performance of ß-trace protein, a novel marker of GFR, would be significantly better in boys than in girls. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: GFR, height, weight, serum creatinine, and ß-trace protein were measured in 755 children and adolescents (331 girls) undergoing (99)technetium diethylenetriamine penta-acetic acid renal scans from July of 1999 to July of 2006. Boys and girls were separated into formula generation cohorts (284 boys and 220 girls) and formula validation cohorts (140 boys and 111 girls). GFR-estimating formulas on the basis of ß-trace protein, creatinine, and height were derived using stepwise linear regression analysis of log-transformed data. The slope of the regression lines of the sex-specific eGFRs were compared. Bland-Altman analysis was used for testing agreement between (99)technetium diethylenetriamine penta-acetic acid GFR and calculated GFR both with this equation in boys and girls as well as previously established Benlamri, White, and Schwartz formulas. RESULTS: In the stepwise regression analysis, ß-trace protein (R(2)=0.73 for boys and R(2)=0.65 for girls) was more important than creatinine (which increased R(2) to 0.81 for boys and R(2) to 0.75 for girls) and height (which increased R(2) to 0.88 for boys and R(2) to 0.80 for girls) in the data generation groups. GFR can be calculated using the following formulas:[Formula: see text]and[Formula: see text]Bland-Altman analysis showed better performance in boys than in girls. The new formulas performed significantly better than the previous Benlamri, White, and Schwartz formulas with respect to bias, precision, and accuracy. CONCLUSIONS: Improved and sex-specific formulas for the estimation of GFR in children on the basis of ß-trace protein, serum creatinine, and height are now available.

Elevated triglycerides may affect cystatin C recovery.

OBJECTIVE: The purpose of this study was to investigate the effect of triglyceride concentration on cystatin C (CysC) measurements. DESIGN AND METHODS: Serum samples collected from 10 nephrology patients, 43 to 78years of age, were air centrifuged to separate aqueous and lipid layers. The lipid layer from each patient was pooled together to create a mixture with a high triglyceride concentration. This pooled lipid layer was mixed with each of the ten patient aqueous layers in six different ratios. Single factor ANOVA was used to assess whether CysC recovery was affected by triglyceride levels. Regression analysis was used to develop a formula to correct for the effect of triglycerides on CysC measurement, based on samples from 6 randomly chosen patients from our study population. The formula was validated with the 4 remaining samples. RESULTS: The analysis revealed a significant reduction in measured CysC with increasing concentrations of triglycerides (Pearson r=-0.56, p<0.0001). The following formula was developed to correct for the effect of triglycerides: Subsequent Bland-Altman plots revealed a bias (mean±1 standard deviation [SD]) of -3.7±15.6% for the data used to generate the correction formula and a bias of 3.52±9.38% for the validation set. CONCLUSIONS: Our results suggest that triglyceride concentrations significantly impact cystatin C measurements and that this effect may be corrected in samples that cannot be sufficiently clarified by air centrifugation using the equation that we developed.