Hyperinsulinaemia in syndrome X: a marker of the syndrome?

Stimulated hyperinsulinaemia is observed in some patients with syndrome X, defined as angina, positive stress test and normal coronary arteriography, and may be involved in the pathogenesis of the syndrome. An increased sympathetic response to exercise may also be pathogenetically involved. However, the diagnostic value of hyperinsulinaemia as a marker of this syndrome has not been defined.

We determined blood glucose and immunoreactive insulin during fasting, at 60 and 120 min after a glucose load of 75g in 21 patients (eight men, 13 women, 53.9 +/- 7.1 years old) with syndrome X and in 21 healthy volunteers matched to the patients for age, sex and body mass index (eight men, 13 women, 51.6 +/- 9.3 years old). Insulin values were related to the rate-pressure product increase at first exercise stage.

The glucose values as well as the insulin values during fasting were similar in syndrome X patients and in controls. However, significantly higher insulin values (mU/l) were observed at 60 (P < 0.01) and 120 min (P < 0.005) in syndrome X patients (median 75.5 and 52, range 43-290 and 6.1-212, respectively) than in controls (median 47.5 and 24.5, range 8-195.6 and 5.2-164, respectively). A considerable overlap of insulin values, however, was observed between the two groups, with abnormal values even during fasting. For a specificity of 95%, an abnormal insulin value had a sensitivity of between 19 and 24% and a diagnostic accuracy of 57-60%. A significant positive correlation was found between insulin levels after the glucose load and the rate-pressure product increment with exercise (60 min, r = 0.60; 120 min, r = 0.65).

Hyperinsulinaemia may be pathogenetically involved in syndrome X patients, in close relation to the higher sympathetic drive that characterizes this syndrome. However, the wide range of insulin values, frequently overlapping with normal values, limits the usefulness of this abnormality as a marker of the syndrome.