Effect of hemolysis, icterus, and lipemia on three acetaminophen assays: Potential medical consequences of false positive results.

BACKGROUND: We evaluated the effect of hemolysis, icterus and lipemia on 3 acetaminophen assays: namely the Syva® EMIT®, the Microgenics DRI® assay, and the Roche assay on a Roche Cobas® c501 or an Integra 800 analyzer.

METHODS: Discarded acetaminophen - free serum samples (blank pool) and patient serum with acetaminophen overdose were used to prepare samples. Three levels of acetaminophen (5, 10, and 30 μg/ml) were evaluated for interference: hemolysis (H index range: 0-1000), icterus (I index range: 0-40), and lipemia (L index range: 0-1000).

RESULTS: Measurements showed that the EMIT® assay was not significantly affected by hemolysis or icterus at all 3concentrations evaluated, but was negatively affected by lipemia at all three levels at 1000 mg/dl intralipids. The DRI® assay was similarly affected by hemolysis and icterus, but lipemia (at 1000 mg/dl intralipids) only affected the 5 μg/ml level. The Roche acetaminophen assay was significantly affected by hemolysis at all three concentrations. It was significantly affected by icterus at 20 mg/dl bilirubin and > 5 μg/ml and at icterus levels of 30 and 40 mg/dl bilirubin at 10 and 30 μg/ml acetaminophen concentrations, respectively. However, the Roche assay was least affected by lipemia.

CONCLUSION: Hemolysis and icterus had insignificant interference on the Syva EMIT® and the DRI® assays for the analysis of acetaminophen, but significant interference effect on the Roche assay. On the other hand lipemia interfered less markedly with the Roche assay. The effect of hemolysis, icterus and lipemia should always be considered. Cautions are warranted when interpreting results for the potential false positive results in the presence of hemolysis and icterus at the concentrations evaluated in this study.