RECIPROCAL ASSOCIATION BETWEEN INSULIN SENSITIVITY AND THE HEMATOCRITIN MAN

In epidemiological studies, a high haematocrit has been associated bot h with increased cardiovascular risk and with hyperinsulinaemia, a sur rogate of insulin resistance. To examine directly the relationship bet ween the haematocrit and insulin sensitivity, we studied 12 healthy vo lunteers and 12 patients with non-insulin-dependent diabetes mellitus (NIDDM) with the use of a 4-hour hyperinsulinaemic [1 mU min(-1) kg(-1 )] isoglycaemic clamp. In the whole group, insulin sensitivity (ns the ratio of insulin-mediated glucose clearance to steady-state plasma in sulin concentrations) was inversely related to the haematocrit (r = 0. 50, P < 0.01). To test whether acute changes in the haematocrit affect insulin sensitivity, in two NIDDDM patients and three healthy subject s the clamp study was repeated after lowering (- 18%) the haematocrit by erythro-apheresis. In all five subjects, the lower haematocrit was associated with slightly reduced (- 7% on average, P = NS) rather than increased insulin sensitivity. We conclude that insulin sensitivity i s inversely related to the haematocrit independently of the glucose to lerance status. The association does not result from acute haemodynami c effects on insulin sensitivity, and may therefore reflect an action of insulin resistance/hyperinsulinaemia on blood viscosity, or the pre sence of a common determinant.