Influence of insulin collection preservatives in postmortem blood: application to a case of insulin aspart suicide.

Insulin aspart (Novorapid ®, NovoMix®, Novolog® and Fiasp®) is a fast-acting analog of human insulin, indicated in the treatment of type I and II diabetes. It is administered before meals to mimic the physiological insulin secretion that follows a rise in blood glucose. Its misuse for the purposes of suicide, murder and in the context of factitious order has often been described. In forensic medicine, the identification of insulin in biological samples has always been complex. In this paper, we present a case of suicide of a 64-year-old man who died after the injection of insulin aspart. He was suffering from terminal lung cancer and left a letter explaining the reasons of his suicide. Four empty Novorapid® pens were found near the body. Body examination was unremarkable and femoral blood was collected in 2 dry Vacutainer tubes (red cap) and 2 sodium fluoride tubed (grey cap). A LC-HRMS method was used to identify and discriminate aspart insulin from human insulin after immunopurification in the blood samples and in the pens. Blood aspart insulin tested positive at 36 and 37 ng/mL in dry tubes, and at 58 and 71 ng/mL in tubes containing sodium fluoride when tested about 3 weeks after collection of the specimens. The contents of the pens also matched with insulin aspart.The stability of insulin in blood is a critical point in the interpretation of the concentrations due to their rapid decrease caused by the activity of proteases in blood. During a degradation study implemented to compare 3 preservatives and dry tubes, suitable insulin aspart stability was observed with EDTA and NaF. Given NaF is standard in forensic toxicology for measuring blood alcohol concentrations, the authors suggest its use for blood collection when insulin intoxication is suspected.