Invisible hemolysis in serum samples interferes in NSE measurement

Introduction: The accuracy of serum neuron-specific enolase (NSE) measurements is critical, particularly in neurologic diseases and cancer. NSE measurements are compromised by slight, even invisible, hemolysis, which can produce apparently higher NSE levels, leading to inappropriate clinical decisions. In this article, we describe this issue and propose a solution for avoiding incorrect results. Methods: Twenty blood samples from donors with NSE values that were within the reference interval were considered. Experimental hemolysis was induced in vitro to examine the relationship between the degree of hemolysis and the increase in serum NSE. The data were then subjected to statistical analysis. Results: There was excellent correlation (r2 0.953) between the degree of hemolysis and the rise in NSE concentration. Each hemolysis unit (equal to 1 mg/dL of free hemoglobin) corresponded to a mean value of 0.29 ± 0.09 ng/mL NSE that was released from red blood cells. Conclusion: The hemolysis index must be measured in every sample with no evident hemolysis before assaying it for NSE. Moreover, if the degree of hemolysis is between 5 and 30 units, the increase in NSE (from 1.5 to 9.0 ng/mL) must be calculated, and the laboratory results should be appended with comments that suggest the approximate rise in NSE.