Features and clinical implications of fasting intact proinsulin to insulin molar (P/I) ratio 1: P/I Ratio vs Pancreatic β cell function in type 2 diabetes mellitus and reference range in subjects with normal glucose tolerance

Using an Intact-Proinsulin Assay® (MLT Research Ltd.), we studied the clinical implications and usefulness of the plasma intact proinsulin to insulin molar ratio (P/I) ratio in morning fasting. Obese (BMI ≥ 25 kg/m ²) adults (age ≥30 years old) with normal glucose tolerance (NGT) had a significantly lower P/I ratio than nonobese adults with NGT. The P/I ratio reference range in nonobese adult NGT was 0.04- 0.31. In nonobese subjects with differing degrees of glucose tolerance, the P/I ratio increased significantly with glucose intolerance severity. The P/I ratio in subjects with type 2 diabetes mellitus treated with diet and exercise alone whose fasting glucose exceeded 126 mg/d/ was significantly higher than in those whose fasting glucose was less than 126 mg/dl. The P/I ratio correlated significant by inverse by with the insulinogenic index in the 75 g oral glucose tolerance test. We found that the P/I ratio is closely related to insulin secretory ability, and may be a simple, easy index for reflecting the impoverishment or functional decline in pancreatic β cells.