What does the fasting test for insulin check?

People are more familiar with fasting blood sugar test. The blood sugar level is used to determine whether a person has diabetes. Some patients need to do a fasting insulin test. Many people do not know what the fasting insulin test is for. This test is mainly used to determine the type of diabetes. Diabetes is mainly caused by absolute or relative insulin deficiency. By measuring fasting insulin, it can be determined whether it is type 1 diabetes or type 2 diabetes.

Insulin is a protein hormone secreted by pancreatic beta cells in the pancreas in response to endogenous or exogenous substances such as glucose, lactose, ribose, arginine, glucagon, etc. Insulin is the only hormone in the body that lowers blood sugar, while promoting the synthesis of glycogen, fat and protein. Insulin measurement is the most reliable method for diagnosing diabetes and distinguishing diabetes types, and is also an important indicator reflecting the storage and secretion function of insulin cells. Clinically, by measuring the secretion levels and curve characteristics of the patient's insulin and C-peptide at various time points during fasting and after meals, we can understand the degree of the patient's pancreatic islet function failure and assist in determining the clinical classification of diabetes. The detection methods of insulin in the body can be summarized into two categories: immunological detection methods and non-immunological detection methods. Immunoassay methods include radioimmunoassay, enzyme-linked immunosorbent assay and luminescent immunoassay; non-immune detection methods include isotope dilution method and high performance liquid chromatography.

Clinical significance

Measuring insulin can help understand pancreatic islet function and determine the type of diabetes. Blood insulin testing is mainly suitable for patients who are not using insulin treatment. Blood can be drawn for measurement when fasting and 2 hours after a meal. Under normal circumstances, the fasting insulin level should be 10-25mU/dL, and the postprandial level should be 4-5 times higher than the fasting level. If insulin levels are significantly reduced, it is called absolute deficiency, which can be seen in type 1 diabetes;

If there is no obvious reduction, it is called relative deficiency, which is due to a malfunction in the process by which insulin exerts its effects, which is common in type 2 diabetes with insulin resistance. Insulin and C-peptide are secreted into the blood in equal molecules. Patients who are treated with insulin clinically have insulin antibodies in their serum, which affect the determination of blood insulin levels by radioimmunoassay. In this case, the state of endogenous insulin secretion can be understood by measuring plasma C-peptide levels.