Serum creatinine determination by high performance liquid chromatography and five automated chemistry analyzers

A sensitive and specific procedure is described for the determination of serum creatinine by reverse phase high performance liquid chromatography. The method involves sample pretreatment with a cation exchange resin followed by the isocratic separation of creatinine and an external standard which are detected by their absorbances at 254 nm. The analytical recovery of creatinine from serum was 99.8 +/- 4.9 percent using this method. The between-day coefficients of variation for creatinine concentrations of 0.83 and 8.63 mg per dl were 3.07 percent and 3.2 percent, respectively. Results obtained with this reference method were compared to results obtained with five automated chemistry analyzers. The results showed that while the comparison methods correlated well with the reference method (r greater than 0.98 in all cases), those comparison methods based on the Jaffe reaction showed negative biases. In some cases, these biases were highly statistically significant. The difference between paired results obtained with some of the automated Jaffe-based assays exceeded 0.20 mg per dl in a substantial number of specimens with creatinine concentration in the range of 0.5 to 2.3 mg per dl. The measurement of acetoacetate concentrations of specimens submitted to our laboratory for serum creatine assays showed that interference by this substance with certain Jaffe-based assays could result in clinically significant false elevations in serum creatinine concentrations.