Your body’s pancreas produces the hormone insulin. It facilitates the body’s energy conversion from food. Antibodies to insulin can develop in certain diabetic patients receiving insulin injections. These people may stop responding to insulin treatment, or they may experience an allergic reaction to insulin. The insulin that is bound by these circulating antibodies prevents it from being used for metabolic processes. For individuals with known or suspected insulin antibodies, the preferred test is free or bioactive insulin. Free and total insulin levels are the same in the absence of insulin antibodies; however, free insulin levels need to be tested in the presence of insulin antibodies in order to accurately determine the amount of insulin in the blood.