Fasting insulin levels as a measure of insulin resistance in American blacks.

Insulin resistance is a common finding in diabetes mellitus, and may serve as a measure of efficacy of therapies for diabetes mellitus: exercise, exogenous insulin, sulfonylureas, and PPAR gamma agonists, and as a possible marker for risk for developing type II diabetes mellitus. The purpose of our study was to compare one measure of insulin resistance, the QUICKI method, which is a calculation of the inverse of the sum of the log of fasting serum glucose plus the log of fasting insulin level, with the observational measure of fasting serum insulin levels. We studied 79 African-American and Caribbean Black patients in an inner-city hospital-based internal medicine practice, 37 of them with type 2 diabetes mellitus and 42 controls. We found that most controls fell within manufacturers proposed reference range for fasting insulin levels. However, about 5% were appreciably above the range, suggesting insulin resistance, despite euglycemia. Among our diabetics there were two subpopulations: those with elevated fasting insulin levels and those with normal or deficient insulin levels. Only about 30% had elevated fasting insulin levels; however, by the QUICKI method, 54% showed insulin resistance. These findings suggest that QUICKI might be more sensitive measure of insulin resistance, while elevated fasting insulin levels may be more specific.