An insulin blood analysis is performed by collecting blood samples every 6 hours during a 72-hour fasting test to measure glucose, insulin, proinsulin, and C-peptide levels. The fasting test ends when glucose levels drop below 45 mg/dL with hypoglycemic symptoms. At the end, additional samples are collected to measure other markers and the patient's response to glucagon. The samples are analyzed using radioimmunoassay or ELISA to measure insulin secretion and processing in the pancreas beta cells. Test results can help identify causes of low blood sugar.