Determination of serum creatinine by Jaffe method and how to calibrate to eliminate matrix interference problems

BACKGROUND: The calibration of Jaffe method for serum creatinine using one serum-based standard complemented with artificial matrix compensating standard's Jaffe-interfering substances allows two-point calibration with results well comparable with enzymatic methods. METHOD: Spectrophotometry was used. RESULTS: Jaffe procedures compensating serum/plasma intereferents by subtracting a constant amount of creatinine poorly overcompensate creatinine in children. Two-point calibration with a pair of primary serum standards certified by the reference measurement procedure (isotope-dilution, mass spectrometry) or with a pair of secondary standards linked to primary materials could provide results well agreeable with enzymatic determination. Such a calibration comprises an absorbance offset corresponding to other-than-creatinine Jaffe-interfering chromogens present in standards in the calibration line, while a two-point calibration combining one standard with physiological saline/water always grossly distorts calibration line. We calculated/prepared artificial serum matrices capable of compensating Jaffe-interfering chromogens in serum standards. The combination of even one standard with its artificial matrix also enables two-point calibration with practically the same results as with a pair of primary standards. CONCLUSIONS: A two-point calibration of Jaffe method for serum creatinine combining only one serum standard with creatinine solution matching standard's allow matrix-present interferents present results well comparable with enzymatic determination, providing the standard is attested/linked to the reference measurement procedure.