Measurement of Creatinine in Whole Blood Samples Supplemented to Achieve Increased Creatinine Concentrations

Abstract

During clinical trials of a new biosensor for measurement of whole blood creatinine, we were unable to obtain sufficient quantities of samples with naturally occurring high creatinine concentrations to validate performance of the sensor across the proposed reportable concentration range for the device [18–1326 μmol/L (0.2–15.0 mg/dL)]. Addition of creatinine to whole blood samples was required to validate performance of the sensor at the high end of the range. We noticed irreproducible results for samples that were supplemented with creatinine to increase the concentration. Like other direct-reading electrochemical biosensors (1), creatinine sensors respond to the molality of creatinine in the sample (amount of creatinine per unit mass of water). It is known that molality of creatinine in erythrocyte fluid is equal to molality in plasma (2) and that creatinine is transported by passive diffusion through the lipid bilayer of the erythrocyte membrane (3). Heparinized blood from a healthy volunteer was centrifuged and the separated plasma supplemented with creatinine to target concentrations of …