TEST FOR INSULIN RESISTANCE

Subjects requiring large amount of insulin to maintain euglycaemia e.g. >150 units or 1.5 units/kg body weight/day, insulin resistance may be postulated. For this insulin is administered intravenously and subcutaneously and the level of glucose and insulin in plasma is measured. Normal fasting insulin concentration are up to 20 mU/L. Hyperinsulinaemic clamp is the reference measure of insulin resistance. In euglycaemic variant of the test, insulin is infused into a peripheral vein so as to raise the plasma insulin concentration to a target range around 60 mU/L. 

The plasma glucose concentration is measured every 5-10 min and glucose is infused peripherally to maintain glucose concentraions within the desired range. When a steady state has been reached (usually 90-120 min), the rate of exogenous glucose infusion needed to maintain the glucose concentration is an index of the glucose clearance rate and of the subject’s insulin sensitivity.

Glucose transporter function can be assayed by incubating cells of interest (e.g. leukocytes, monocytes, adipocytes) with a non-metabolizable glucose analog such as 2-deoxyglucose. The cellular content of the glucose analogue after a given time provides a measure of glucose transporter function.  

MEASUREMENT OF β- CELL FUNCTION

Measurement of plasma C-peptide concentration can be done. Elevated fasting plasma proinsulin indicates subjects with abnormal beta cell function, even if glucose tolerance is normal.