A-119 Performance Evaluation of a New Enzymatic Creatinine Assay on Mindray Clinical Chemistry BS-2800M Analyzer With Excellent Accuracy
Authors: Zheng X , Wang H , Wu M , Liu Z , Wang J , Jiang M , Dai J 
Published: September 2023

Abstract

Background
Serum creatinine is used to estimate glomerular filtration rate (GFR) and monitor the progression of renal diseases. Accuracy and precision for this assay is very important. False estimates of serum creatinine were found in some cases due to the interference by exogenous and endogenous substances in addition to inadequate standardization. Substances, such as lipid, bilirubin, Hemoglobin (hemolysis) and ascorbic acid have been recognized as the cause of interference. Other endogenous substances such as paraprotein may also cause interference that has rarely been systematically studied. This study specifically evaluated such performance for the new enzymatic creatinine assay, in addition to the general assay characteristics.

Method
This assay is based on the sarcosine oxidase creatinine method with dual reagents. The reagent formulation was optimized. Concentrations are calculated from a calibration curve with a calibrator. Assay precision was evaluated using EP05-A3. The assay linearity was evaluated following EP06-Ed2. On board stabilities were tested with opened reagent for the duration of the testing. Accuracy studies were conducted against in-house ID-LC-MS/MS reference method that is calibrated with SRM 914a and validated by SRM 967a. Interference testing was run in accordance with EP07-Ed3. Paraprotein interference was evaluated by serum samples with high concentration of globulin and serum samples from patents with rheumatoid diseases and hematologic cancers. All these samples were measured by three commercial creatinine methods in parallel. Ten samples were found with discrepant results. Target values for these 10 samples and other 8 normal samples were obtained by the ID-LC-MS/MS reference method.

Results
The repeatability and within-lab CVs on the BS-2800M system were found ranging from 0.5% to 2.0% and 1.0% to 3.5% respectively, at creatinine concentrations of ∼85 µmol/L (0.96 mg/dL) and approximately372 µmol/L (4.21 mg/dL). The assay linearity was from 10 to 7000 µmol/L. The reagent onboard stability was found to be for 28 days. The assay (Y) showed excellent accuracy when it compared with ID-LC-MS/MS reference method(X): Y = 1.0339X-3.5404 (r = 0.99, n = 31). There is no significant interference (&lt;±10%), at creatinine concentration of 53 µmol/L with bilirubins up to 20 mg/dL, hemolysate hemoglobin up to 200 mg/dL, Intralipid up to 1000 mg/dL, triglycerides up to 2000 mg/dL, and ascorbic acid up to 30 mg/dL. Three hundred patient samples with high globulin and 200 samples from patients with rheumatoid diseases and hematologic cancers were used for paraprotein interference study. With these samples, the average bias vs Roche enzymatic creatinine method was found less than 2.5%. The recoveries of 18 samples were compared with ID-LC-MS/MS reference method. The mean bias in that comparison was −4.1%.

Conclusion
The new Mindray creatinine assay demonstrates excellent accuracy and anti-paraprotein interference performance on BS-2800M system. It is suitable for the use in clinical laboratories.