Hemolysis index to detect degree of hydroxocobalamin interference with common laboratory tests

Cyanokit^® (hydroxocobalamin OHCo) is the recommended treatment for cyanide poisoning. OHCo is a red chromophore and may cause interference with some biochemical measurements. In this study, we assessed the possible interference of Cyanokit on several cooximetric and plasma biochemistry tests and then determined the possible mathematical correction for some analytes. We studied the possibility of detecting and evaluating the degree of interference with the hemolysis index (HI) provided by our autoanalyzer because it is not possible to measure the OHCo concentration in conventional laboratories.

Several pools of plasma samples spiked with increasing concentrations of OHCo were prepared. Each one was compared to the pool without interferent. Interference was considered when the bias was more than 10%. An interferograph was developed for those analytes with significant interference. The correlation between interference agent concentration and HI was calculated by Spearman correlation coefficient. We used multiple regression analysis to determine the mathematical correction for amylase, creatinine, and lactate.

We detected significant interference in the amylase, carboxyhemoglobin, creatinine, creatine kinase, bilirubin, lactate, and total protein measurement. The HI was positively correlated with OHCo concentration. Corresponding equations for estimating lactate and creatinine concentrations were obtained.

OHCo interferes with many laboratory assays in an unpredictable way making some results invalid and confounding clinical decision making. We can detect and evaluate the degree of interference with the HI. We can still estimate real creatinine and lactate levels using the regression equation obtained in this study.