Interference Testing of the Creatinine Sensor in the ABL837 FLEX Analyzer

Abstract

A newly developed creatinine sensor for the ABL837 FLEX blood gas analyzer (Radiometer Medical ApS, Copenhagen, Denmark) is based on the enzymatic conversion of creatinine by 3 enzymes. This conversion leads to the formation of hydrogen peroxide in the final stage, which is detected by an amperometric electrode. The results of an interference test of the creatinine sensor are presented as well as data on imprecision and bias. The interference test was performed according to the Clinical and Laboratory Standards Institute (formerly National Committee for Clinical Laboratory Standards) protocol EP7-A2 on serum with a normal creatinine concentration of 50 to 100 μM (0.57-1.13 mg/dL). Fifty-four different endogenous and exogenous substances were tested. Serum samples were spiked with the substance tested (test sample) and were compared with a control sample without the substance. Each substance was analyzed 3 times, and the maximum allowable difference was defined to be 8 μM. The conclusion of the interference test is that no substance demonstrated a higher degree of interference than the allowable 8 μM, although interference from Intralipid at high concentration (10 g/L) cannot be excluded. For only one analyte, d(+)-glucose, a significant difference existed between test and control sample (P < 0.05). Eight other substances demonstrated a higher SD for the test or control sample than 2.5 μM, which affected the difference between creatinine in control and test sample, although the differences did not in any case exceed 8 μM. The repeatability in the normal as well as in the pathological creatinine range was 1.1% to 1.5% (CV%) in whole blood (n = 45) and 0.9% to 1.1% in plasma (n = 80, duplicate samples for 20 days).