Comparison of methods of estimating creatinine clearance in pediatric patients

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Abstract

Purpose.

A retrospective study was conducted to compare various methods of measuring serum creatinine (SCr) values for use in pediatric renal function assessments, including a method aligned with a recently implemented national SCr testing standard.

Methods.

Demographic, medication-use, and selected laboratory data were collected from the hospital records of a sample of pediatric patients (n = 91) who underwent 12- or 24-hour timed urine collection for determination of creatinine clearance (CLcr) over a 2-year period. Documented CLcr values measured via the timed urine collection method were compared with investigator-calculated estimates of CLcr or glomerular filtration rate (GFR) derived using 3 SCr-based methods: the Counahan–Barratt equation; the original Schwartz equation; and the “bedside IDMS-traceable Schwartz equation,” a modified version of the Schwartz equation reflecting the recent shift toward isotope dilution mass spectrometry (IDMS) methods of SCr measurement, which have been found to yield SCr values 10–20% lower than those derived by older methods, potentially resulting in GFR overestimation if traditional formulas for estimating GFR are used.

Results.

Comparisons of timed urine collection–derived CLcr values with CLcr values derived from the 3 comparator equations indicated significant levels of bias in all cases, with calculated correlation coefficients of 0.71 for the original Schwartz equation, 0.72 for the bedside IDMS-traceable Schwartz equation, and 0.72 for the Counahan–Barratt equation.

Conclusion.

Pediatric CLcr values calculated using the original Schwartz, bedside IDMS-traceable Schwartz, and Counahan–Barratt equations were well correlated, but none of the 3 equations yielded values that correlated well with CLcr values derived via the gold-standard method of timed urine collection.

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