Free insulin concentrations in immediately extracted plasma samples and their relationships to clinical and metabolic parameters in insulin-treated diabetic patients.

The relationships between free insulin and various clinical and metabolic parameters in insulin-treated diabetic patients are still not clear, possibly because of the technical difficulties in measuring free insulin. Recently, it has been demonstrated that in the presence of insulin antibodies only immediate centrifugation of blood and extraction of insulin antibodies provide an accurate evaluation of in vivo free insulin concentrations. In this study we evaluated the relationships between free and bound insulin levels, insulin antibodies, metabolic control and insulin requirement in 38 insulin-treated diabetic patients, in whom plasma free insulin was assayed in immediately processed samples. The main findings of our study are as follows. Free insulin concentrations ranged from 2.5 to 54 microU/ml; no difference was found between males and females; the unbound hormone level was inversely correlated to fasting plasma glucose (p less than 0.01) and HbA1c (p less than 0.02); a positive correlation was shown between free insulin and daily insulin dose; finally, free insulin concentrations were not correlated with insulin antibody binding.