The Case of the Insolent Insulin

    A patient was admitted to the emergency room of a hospital in insulin shock, a condition caused by excess insulin in the blood. Radioimmunoassay (RIA) measured high levels of insulin in his blood, as expected. His physicians first suspected an insulinoma, a cancer of the pancreas that would cause over-secretion of insulin. However, the biopsy was negative. The patient stabilized, and was released. Several weeks later, the patient showed up in the same ER, again in insulin shock. The Kettering Professor of Medicine asked his Tech to adjust the RIA to measure preproinsulin as well as insulin. This time, the patient tested positive for insulin as before, and also tested negative for preproinsulin.