Performance verification and sigma metrics of creatinine assays

Abstract

Introduction: Creatinine enzymatic method is more accurate but its own higher cost is the main reason why the use of Jaffe assays is still in practice. The verification step is performed because assay procedure confirms to the manufacturer’s claims in the end users’ setup. Desirable specification based on biological variation gives Allowable Total Error (ATE) and Sigma metrics provides summative evaluation of method performance. Objectives: Verification of manufacturer’s precision claims. Calculation of bias, Total Analytical Error (TAE) and sigma metrics. Materials and Methods: Modified Jaffe’s (No deproteinization) and enzymatic creatinine Erba XL liquid pack on Erba EM360 fully auto analyser were used. Intra assay and inter assay imprecision done on 20 replicates each. The estimates of bias uses data from precision experiment. Results & Discussion: The performance of jaffe’s and enzymatic serum creatinine is comparable to manufacturer's stated claimed value and are within desirable specification based on biological variation. The bias calculated in both assays is less than allowable bias. Total Analytical Error (TAE) is less than Allowable Total Error (ATE). Both the methods overall showed ATE ? bias + 4 SD. Within-run showed ATE ? bias + 5 SD complying Six Sigma concepts. Conclusion: Both Jaffe’s and enzymatic creatinine assays gives good performance and better sigma metrics. This makes enzymatic method a better choice due to inherent advantages such as increased accuracy and less interference if cost is neglected. Keywords: Allowable Total Error, Bias, Creatinine, Imprecision, Sigma metrics, Total Analytical Error.