Serum creatinine levels are significantly influenced by renal size in the normal pediatric population

Abstract

Background and objectives: Clinical and experimental data have shown that differences in nephron endowment result in differences in renal mass and predisposition to chronic renal failure, hypertension, and proteinuria. We hypothesized that a significant proportion of the variance in GFR, as estimated by serum creatinine, is attributable to differences in renal size in normal children.

Design, setting, participants, & measurements: A total of 1748 normal renal ultrasounds that were performed in children older than 6 months were reviewed. For each ultrasound, serum creatinine, serum blood urea nitrogen, and systolic and diastolic office BP were recorded. Renal size was evaluated as a function of renal length and thickness. All data were normalized for height, weight, age, and gender.

Results: When expressed as SD scores, a significant correlation was found between kidney size and serum creatinine (P < 0.0001) and between kidney size and serum blood urea nitrogen (P < 0.002). When dividing kidney size data per quintiles, a difference of 0.51 SD score in serum creatinine was observed between the lowest and highest quintile. No significant correlation was found with office BP measurements.

Conclusions: These data show that, even in the normal pediatric population, differences in renal function are significantly explained by differences in renal mass. Methodologic limitations of this study are likely to underestimate this relationship.

Figure 1.

Data normalization process. The data normalization process is shown for KS and for serum creatinine. Nonlinear equations were used to calculate the best fitting function of each parameter as a function of height, weight, age, and gender, and residuals were corrected for heteroscedasticity (A and D). This allowed expressing data as SDS that followed a normal distribution (B and E). Once expressed as SDS, values were homogeneously distributed on both sides of the mean, independently of height, weight, age, and gender (C and F). Thinner lines in A, C, D, and F indicate +1SD and −1SD. The same process was used to generate SDS for BUN, SBP, and DBP (data not shown). ^aKS was calculated using a best-fitting model (equation 1 in online supplementary material).

Figure 2.

Distribution of SDS for serum creatinine, serum BUN, SBP, and DBP per quintiles of KS. Quintiles are expressed in SDS (see Figure 1B): 1st quintile, < −0.85; 2nd quintile, from −0.85 to −0.22; 3rd quintile, from −0.23 to +0.24; 4th quintile, from +0.25 to +0.84; 5th quintile, > +0.84.