THE EFFECT OF PHLEBOTOMY-INDUCED HEMOLYSIS ON INSULIN LEVEL DETERMINATION.

ABSTRACT

OBJECTIVE: To examine the effect of phlebotomy-induced hemolysis on serum insulin and C-peptide measurement by an immunochemiluminometric assay. METHODS: As part of a study designed to evaluate ß-cell function in a group of adults with newly diagnosed type 2 diabetes, we tested insulin and C-peptide levels in 1,048 samples. In order to evaluate the effect of phlebotomy-induced hemolysis, we determined insulin and C-peptide levels simultaneously in hemolyzed and nonhemolyzed samples. RESULTS: Forty-seven (4.5%) of the 1,048 samples were affected by hemolysis. In 26 cases, we had paired hemolyzed and nonhemolyzed serum samples that allowed a simultaneous comparison. We found that all degrees of hemolysis led to a significant decrease in insulin level. In hemolyzed serum, the median (interquartile range) of the insulin was 5.6 (1.8 to 24.3) mIU/L, versus 21.3 (11.4 to 48.5) mIU/L in nonhemolyzed serum, representing a 25 to 98% loss. This phenomenon was not found for C-peptide levels. CONCLUSION: Clinicians have to be aware that even a mild degree of phlebotomy-induced hemolysis has a significant effect on serum insulin level determination, which can lead to misinterpretation of test results. This finding has important implications, especially in the evaluation of suspected cases of hyperinsulinemic hypoglycemia.