Data mining of reference intervals for serum creatinine: an improvement in glomerular filtration rate estimating equations based on Q-values

Abstract

Objectives: Glomerular filtration rate (GFR) estimating equations based on rescaled serum creatinine (SCr/Q) have shown better performance, where Q represents the median SCr for age- and sex-specific healthy populations. However, there remains a scarcity of investigations in China to determine this value. We aimed to develop Chinese age- and sex-specific reference intervals (RIs) and Q-values for SCr and to validate the equations incorporating new Q-values.

Methods: We included 117,345 adults from five centers for establishing RIs and Q-values, and 3,692 participants with reference GFR (rGFR, ^99mTc-DTPA renal dynamic imaging measurement) for validation. Appropriate age partitioning was determined using the decision tree method. Lower and upper reference limits and medians were calculated using the refineR algorithm, and Q-values were determined accordingly. We evaluated the full age spectrum (FAS) and European Kidney Function Consortium (EKFC) equations incorporating different Q-values considering bias, precision (interquartile range, IQR), and accuracy (percentage of estimates within ±20 % [P20] and ±30 % [P30] of rGFR).

Results: RIs for males were: 18-79 years, 55.53-92.50 μmol/L; ≥80 years, 54.41-96.43 μmol/L. RIs for females were: 18-59 years, 40.42-69.73 μmol/L; 60-79 years, 41.16-73.69 μmol/L; ≥80 years, 46.50-73.20 μmol/L. Q-values were set at 73.82 μmol/L (0.84 mg/dL) for males and 53.80 μmol/L (0.61 mg/dL) for females. After validation, we found that the adjusted equations exhibit less bias, improved precision and accuracy, and increased agreement of GFR categories.

Conclusions: We determined Chinese age- and sex-specific RIs and Q-values for SCr. The adjustable Q-values provide an effective alternative to obtain valid equations for estimating GFR.

Keywords: creatinine; glomerular filtration rate (GFR); kidney function tests; reference interval.