Hemolysis is a major cause of variability in insulin measurement during oral glucose tolerance test in children

Background: The oral glucose tolerance test (OGTT) is widely employed to evaluate insulin resistance in children with growth hormone deficiency. Due to the difficulty in blood sampling, hemolysis is a frequent pre-analytic interference. The present study was performed to characterize the effects of hemolysis on insulin assays, in order to assess the need to generate automatic hemolysis reports and/or to reject hemolyzed samples. Methods: Insulin plasma levels were measured using a Siemens ADVIA Centaur on samples obtained from children with suspected GH deficiency at risk for insulin resistance during OGTT. Results: The presence of hemolysis (with a concentration of free hemoglobin above 75 mg/dL) promotes a dose- and time-dependent decrease in immunoreactive insulin at any time-point evaluated during OGTT. As a consequence, the variability of insulin is particularly high (often exceeding 100% of the mean value) as compared to that of glucose. This variability is markedly reduced after removal of the hemolyzed samples. Conclusions: When hemolysis is not taken into account a misinterpretation of insulin secretion pattern can occur. It is therefore imperative to: (i) analyze blood samples immediately after sampling, (ii) reject samples with a concentration of free hemoglobin equal to or above 125 mg/dL and (iii) always report the possible interference.