Most patients receiving insulin will eventually form antibodies that bind insulin. These antibodies may or may not affect the activity and metabolism of insulin. Free and total insulin is a test to measure the fraction of insulin that is bound by antibodies and to measure total insulin after the removal of antibodies by special preparation. Free insulin represents a portion of total insulin unbound by insulin binding antibodies in the circulation. This fraction serves as a measure of biologically active insulin and provides an indication of the true relationship between insulin dose and blood glucose in diabetic patients. Levels of free insulin correlate inversely with periods of hypoglycemia or hyperglycemia in diabetic patients, where total insulin can remain fairly constant.