Cross-reactivity of insulin analogues with three insulin assays

Background Immunometric assays have recently shown higher specificity in the detection of human insulin than radioimmunoassays with almost no cross-reaction with proinsulin or C peptide. The introduction of the new insulin analogues on the market, however, has raised the need to define their cross-reactivity in these assays. Several studies have been published in this regard with different results. Methods The analogues studied were insulins lispro, aspart, glargine, detemir, and glulisine. Insulin concentrations were measured in Immulite (R) 2000 and Advia Centaur (R) XP (Siemens Healthcare Diagnostics), and Elecsys (R) Modular Analytics E170 (Roche). All samples were processed 15 times in the same analytical run following a random sequence. Those samples which showed statistically and clinically significant changes in insulin concentration were reprocessed using increasing concentrations of analogue, and this was done twice, using two different serum pools, one with a low concentration of insulin and one with a high concentration of insulin. Results In the Elecsys (R) E170 analyser, glargine showed statistical changes (comparison of mean concentrations with p<0.05) and clinically significant changes in measured insulin (percentage difference 986.2%>reference change value: 59.8%), and the interference increased with increasing concentrations of analogue; the differences were not significant in the case of the other analogues. In the Advia Centaur (R) and Immulite (R) 2000 only the results for glulisine did not present significance (percentage difference 44.7%