[How to assess insulin action in man in research and clinical practice]

Various methods have been proposed to assess insulin action in vivo, from the most complex to the simplest. All methods are based on the comparison of plasma concentrations of glucose and insulin, but can be differentiated by some important characteristics: evaluation in the basal state, after administration of exogenous insulin or after stimulation of insulin secretion; measurement in conditions of normo, hyper- or hypoglycaemia; and assessment using or not a modeling approach. For research purpose, the most informative techniques, such as the "euglycaemic hyperinsulinaemic clamp" or the intravenous glucose tolerance test combined with the minimal model approach, should be preferred. Easier tests may be used as alternative approaches, such as the fixed insulin-glucose infusion or the continuous infusion of glucose with model assessment (CIGMA). In daily practice, the clinician can often use simpler indices, such as fasting insulin concentrations, eventually analysed in comparison with corresponding glucose levels using the HOMA method. The only easy to perform dynamic maneuver is the short insulin tolerance test, but it is subject to several criticisms. As every approach for measuring insulin action has its own advantages and disadvantages, the selection essentially depends on studied populations (diabetic or not), primary objectives and, most importantly, available means.