Stability of proinsulin in whole blood

Proinsulin, the precursor for insulin, is secreted in higher concentrations when beta-cells are under stress and previous studies have shown that elevated proinsulin could be used as a marker for individuals in a pre-diabetic state. The aim of this study was to assess the stability of proinsulin across a wide concentration range (3-882 and 2-187 pmol/L; total and intact proinsulin respectively) in whole blood to determine whether it could be used in routine clinical care. 51 subjects (26 normal glucose tolerance, 17 impaired glucose tolerance and 8 type 2 diabetes) had blood taken into EDTA tubes at 0, 60 & 120 min following a glucose load. The samples were kept at room temperature (similar to 20 degrees C) with aliquots taken, centrifuged and frozen at 0, 24, 48 and 72 h. Comparison of the combined data (pre and post-glucose load) of baseline with 72 h as a percentage of baseline gave an average of 123% (95% CI: 119-127) and 107% (95% CI: 105-109) for total and intact proinsulin respectively. A small change in the stability of total proinsulin was observed whilst there was no clinical difference over the 72 h period for intact proinsulin.