Comparison between surrogate indices of insulin sensitivity and resistance, and the hyperinsulinaemic euglycaemic glucose clamp in urban South African blacks with and without coronary artery disease.

Coronary artery disease (CAD) and diabetes mellitus (DM) are increasing in urban black South Africans during their transition from a rural to a western lifestyle. Insulin resistance is associated with CAD and DM. Fasting-based indices [homeostasis model assessment of insulin resistance (HOMA IR), log HOMA IR, and quantitative insulin sensitivity check index (QUICKI)] were calculated and their correlations with the glucose disposal rate (M) obtained from the hyperinsulinaemic euglycaemic glucose clamp were compared in 40 patients with CAD and 20 patients without CAD. Normal glucose tolerance (NGT), impaired glucose tolerance (IGT) and DM were categorised using the oral glucose tolerance test. M and QUICKI were lower in patients with CAD (p<0.0001 and p<0.02); HOMA IR and log HOMA IR were higher (p<0.02). M and QUICKI decreased and HOMA IR and log HOMA IR increased progressively across the NGT, IGT and DM categories in patients with and without CAD. Glucose concentrations increased across the glucose tolerance categories in patients with CAD (p<0.001) and without CAD (p<0.01). Linear regression analysis revealed significant correlations between M and log HOMA IR (r=-0.3412; p<0.02) and QUICKI (r=0.4078; p<0.003), and between waist circumference (WC) and log HOMA IR (r=0.4637) and QUICKI (r=-0.4680) both p<0.001. We concluded that patients with CAD were more insulin resistant than patients without CAD. As glucose tolerance declined, insulin resistance worsened. Log HOMA IR and QUICKI were comparable to the hyperinsulinaemic euglycaemic glucose clamp and these surrogate indices provided a valid method to estimate insulin sensitivity/resistance in our patients.