Plasma free insulin concentrations: keystone to effective management of diabetes mellitus in children.

In patients with insulin-dependent diabetes, the therapeutic effect of prescribed insulin is routinely judged by the response of the blood glucose concentration. Measurement of both free and bound circulating insulin indicates that neither total nor free insulin concentrations correlate with the prescribed insulin dose. Errors of insulin administration may account for this discrepancy. Free insulin rather than total insulin values determine the plasma glucose concentration and the degree of long-term glycemic control as reflected by levels of hemoglobin A1C. Diabetic ketosis and ketoacidosis are strongly associated with absence of free-circulating insulin. Knowledge of plasma-free insulin values is useful in the management of insulin-dependent diabetes mellitus.