High-performance liquid-chromatographic measurement of plasma creatinine in newborns

This HPLC method for measuring plasma creatinine is based on cation-exchange chromatography and is particularly suitable for use with specimens from babies. A short chromatographic run is performed after simple protein precipitation with zinc sulfate and addition of an internal standard, N-methylnicotinamide. The standard curve for the method is linear up to 200 mumol/L, and analytical recovery of added creatinine is between 101% and 103%. Between-batch precision (CV) is less than 3% for mean creatinine values of 103 and 164 mumol/L. The method is free of interference from other metabolic components and drugs commonly used in neonates in routine clinical practice. Using specimens from neonates, I compared this method with a routinely used automated alkaline picrate method (from Randox Labs., performed on a Cobas MIRA analyzer). Linear-regression analysis yielded a correlation coefficient of 0.90, a slope of 1.00, and an intercept of +0.8 mumol/L. This HPLC method for creatinine should be of use in those circumstances where the alkaline picrate method is known to produce dubious results; however, the latter method is probably more suitable for routine use.