Calculation of the estimated glomerular filtration rate using the 2021 CKD-EPI creatinine equation and whole blood creatinine values measured with Radiometer ABL 827 FLEX

Abstract

Objectives: Estimated glomerular filtration rate (eGFR) can be calculated using serum/plasma creatinine measured with automated chemistry analyzers. It is unclear whether eGFR can be calculated using creatinine values measured in whole blood (WB creatinine). The aim of this study is to determine the comparability between the eGFR calculated using WB creatinine and plasma creatinine. Methods: Blood samples from 1,073 patients presented to the emergency department (ED), perioperative areas, intensive care unit (ICU) or nuclear medicine were used to determine the accuracy of WB creatinine. For each sample, WB creatinine was first measured with Radiometer ABL827 FLEX blood gas analyzer, then plasma creatinine was measured with Roche Cobas702 chemistry analyzer after samples were centrifuged. In a subset of 247 samples with the information of age and sex, whole blood eGFR (WB eGFR) and plasma eGFR were calculated using WB creatinine and plasma creatinine and the 2021 chronic kidney disease epidemiology collaboration (CKD-EPI) creatinine equation, respectively. Results: WB creatinine correlated with plasma creatinine linearly with a slope of 1.06 and an intercept of -0.01. The coefficient of determination (R2) was 0.99. WB eGFR correlated with plasma eGFR linearly with a slope of 0.95, intercept of -1.63, and R2 of 0.97. Comparing to plasma eGFR, the sensitivity and specificity for WB eGFR to identify those with high risk (eGFR<30 mL/min/1.73 m2) and low risk (eGFR>45 mL/min/1.73 m2) for kidney injuries was 100 and 92.2%, respectively. The overall concordance in classifying the four stages of kidney damage between WB eGFR and plasma eGFR was 87.9%. Conclusions: WB creatinine measured with Radiometer ABL827 Flex can be used to calculate eGFR using the 2021 CKD-EPI creatinine equation. The sensitivity and specificity for WB eGFR to identify those with high and low risks for potential kidney injuries are acceptable in patients needing rapid assessment of their kidney functions.