A-369 Evaluation of a Point-of-Care Whole Blood Creatinine Assay and eGFR Concordance using the CKD-EPI 2021 Equation
Authors: Elonda Y , Zwaan K , Xu C 
Published: September 2023

Abstract

Background
Estimated glomerular filtration rate (eGFR) from serum creatinine is considered a better assessment of renal function than serum creatinine alone. Patients with chronic kidney disease have a higher risk of developing contrast-induced nephropathy (CIN). GEM Premier ChemSTAT (Instrumentation Laboratory, Bedford, USA) whole blood (WB) creatinine assay along with eGFR reporting capability per the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) 2009 eGFR equation is now available and could provide a quick point-of-care (POC) screening test alternative to the lab assay for patient risk management. Currently the CKD-EPI 2009 formula for non-AA population has been used to estimate eGFR in our institution. Recently the CKD-EPI 2021 equation without race adjustment has been recommended by multiple professional societies. The goal of this clinical evaluation was to compare the analytical performance of the ChemSTAT WB creatinine assay and the clinical concordance of eGFR to an established lab method by CKD-EPI 2021 equation.

Methods
Remnant heparinized WB samples along with age and gender were obtained. The WB samples were analyzed on the GEM Premier ChemSTAT and the plasma assayed on an Architect analyzer (Abbott Laboratories, Lake Forest, USA) as the reference method. The eGFR based on the CKD-EPI 2009 equation were obtained for both WB and plasma creatinine. The eGFR based on CKD-EPI 2021 equation were retrospectively calculated based on WB and plasma creatinine, age and gender. The clinical concordance of categorizing patients with abnormal kidney function (eGFR &lt; 60 ml/min/1.73 m2) and overall concordance of patients (eGFR &lt; 60 + eGFR≥60) was assessed for WB vs plasma eGFR. Error grid analysis was performed for eGFR as described by Snaith et al. (1) to identify the impact of discordant results between WB and plasma eGFRs.

Results
A total of 60 patient samples were analyzed, median age (SD) = 68.5 (15.2), 53.3% female. The WB ChemSTAT creatinine assay correlated well with the Architect across the tested ranges with regression results of: ChemSTAT_Creatinine (μmol/L) = 1.1099*Architect_Creatinine – 16.0, r = 0.990. A small mean bias (SD) of -3.0 (22.6) μmol/L was observed between ChemSTAT and Architect from the Bland-Altman analysis. When identifying patients with abnormal kidney function (eGFR &lt; 60), ChemSTAT WB eGFR showed 84% (21/25) concordance against the plasma eGFR. An overall clinical eGFR concordance of 88% (53/60) was observed for ChemSTAT. The error grid analysis indicated 100% (60/60) of ChemSTAT WB eGFRs (Zones A and B combined) had no implication to clinical management. Mean biases (SD) from reported CKD-EPI eGFR 2021 vs 2009 equation of 3 (1.6) and 2 (2.6) were observed from Architect plasma creatinine and ChemSTAT WB creatinine, respectively.

Conclusions
Strong correlations were observed between the ChemSTAT WB POC creatinine assay and eGFR versus the lab method. Based on the high clinical concordance of WB eGFR with CKD-EPI 2021 equation and low mean bias, GEM Premier ChemSTAT demonstrated good performance as POC method for rapid and lab quality renal function assessment.