How Good a Marker Is Insulin Level for Insulin Resistance?

TLDR

Epidemiologic studies have linked fasting and postload insulin levels to coronary heart disease risk, assuming these levels reliably indicate insulin resistance, yet this assumption has not been systematically examined. The study aimed to assess how well insulin levels measured after an oral glucose load correlate with insulin resistance quantified by the euglycemic hyperinsulinemic clamp across a spectrum of glucose tolerance. Researchers measured insulin responses to a glucose load and quantified insulin resistance using the clamp technique in 132 subjects (50 normal, 28 impaired, 54 non‑insulin‑dependent diabetes) randomly selected from 1987–1989 Kuopio population studies. In normoglycemic participants, fasting and postload insulin strongly correlated with insulin resistance (r = –0.58 to –0.74), whereas in impaired glucose tolerance and non‑insulin‑dependent diabetes the correlations were weaker, with only fasting insulin remaining significantly correlated (r = –0.47 and –0.48); thus, fasting insulin should be used as the marker of insulin resistance in population studies.

Abstract

Epidemiologic studies have correlated fasting and postload insulin levels with the risk of coronary heart disease, assuming that insulin levels are reliable markers of insulin resistance. However, this assumption has not been systematically studied. The author measured insulin response to an oral glucose load and quantitated insulin resistance using the euglycemic hyperinsulinemic clamp technique to evaluate the correlation between insulin level and the degree of insulin resistance in individuals with varying degrees of glucose tolerance. Subjects were randomly selected from previous population studies done in 1987–1989 at the Department of Medicine of the University of Kuopio in east Finland. Altogether, 50 subjects with normal glucose tolerance, 28 with impaired glucose tolerance, and 54 with non-insulin-dependent diabetes mellitus were studied. Correlations of insulin resistance (whole-body glucose uptake in clamp studies) with fasting or postload insulin levels were remarkably consistent, ranging from −0.58 to −0.74 (p < 0.01) in subjects with normoglycemia. In contrast, corresponding correlations were substantially weaker in subjects with impaired glucose tolerance and non-insulin-dependent diabetes. Among these subjects, only the fasting insulin level correlated significantly with insulin resistance (−0.47, p < 0.05 and −0.48, p < 0.01, respectively). The authors conclude that in population studies, only the fasting insulin level should be used as a marker of insulin resistance, particularly in subjects with abnormal glucose tolerance.