Analytical evaluation of Radiometer ABL90 FLEX PLUS enzymatic creatinine assay

Background: The diagnosis of kidney disease strongly relies on accurate and reproducible measurements of creatinine, even when performed with point of care testing (POCT) devices. Therefore, this study aimed at performing a comprehensive evaluation of the analytical performance of a creatinine enzymatic assay on the Radiometer ABL90 FLEX PLUS. Methods: This analytical evaluation encompassed the assessment of intra-assay, inter-assay and total imprecision, along with linearity on routine lithium-heparin plasma samples. Method comparison was also carried out using results generated with Radiometer ABL90 FLEX PLUS in heparinized whole blood and those obtained in paired heparinized plasma with a reference enzymatic creatinine assay and a Jaffe method, both assayed on Roche Cobas c702. Results: The intra-assay imprecision of Radiometer ABL90 FLEX PLUS creatinine enzymatic assay was between 0.33–1.26%, the inter-assay imprecision between 0.64–1.78%, thus yielding a total imprecision of 0.79–1.99%. The linearity of the assay was excellent (r=1.000; P<0.001) in a range of plasma creatinine concentrations between 47 and 445 µmol/L. An excellent correlation was found between creatinine measured on heparinized whole blood using Radiometer ABL90 FLEX PLUS enzymatic assay and plasma creatinine assayed on the same centrifuged samples using both Roche Cobas c702 creatinine enzymatic assay (r=0.99 and r=0.98; both P<0.001). Compared to both Roche Cobas assays the percent bias was ≤1% and the agreement at chronic kidney disease (CKD) diagnostic thresholds was ≥94%. Conclusions: The results of this analytical evaluation confirm that Radiometer ABL90 FLEX PLUS creatinine enzymatic assay is at least as suitable as a conventional clinical chemistry enzymatic technique for routine and urgent diagnosis of kidney diseases.