Which enzymatic creatinine tests to use in neonates? interference verification of three creatinine methods

Abstract

Aim Interferences with creatinine measurements may result in inaccurate estimations of the glomerular filtration rate, particularly in children and neonates. We investigated the impact of common interferences on three creatinine methods. Methods Pooled serum samples at three creatinine concentrations were spiked with HbA, HbF, unconjugated bilirubin and Intralipid and measured in duplicates with Roche’s compensated, rate-blanked, kinetic Jaffe and enzymatic methods and on Radiometer’s ABL827 analyser. Absolute and relative differences between spiked and unspiked specimens were compared to interference indices recommended by manufacturers. Our interference criterion was ±8% recovery of unspiked samples, based on the Royal College of Pathologists of Australasia Quality Assurance Program’s (RCPA QAP) allowable limits of performance. Results The degree of HbA and HbF interference in the Roche Jaffe and enzymatic methods depended on creatinine concentration. The manufacturer’s single HbA haemolysis index (1000 Jaffe; 800 enzymatic) was only applicable when creatinine was >95 μmol/L. When creatinine was Conclusion Creatinine method interference by haemolysis and bilirubin can be additive, therefore we found the Radiometer ABL 827 enzymatic method the most reliable for such specimens. Interference indices provided by manufacturers should be critically evaluated at different analyte concentrations, and single cut-off values cannot be universally applied to all specimens without verification.