Insulin - Fasting
What is Insulin-F?
Insulin is a hormone secreted by the beta cells of the pancreas. It helps to maintain normal blood glucose levels by regulating glucose uptake and storage by body cells. The Fasting Insulin Test measures the levels of insulin in blood after a fasting period.
Why is Insulin-F done?
The Fasting Insulin Test is performed:
· To help determine the cause of low blood sugar (hypoglycemia)
· To determine the proper production of insulin by the pancreas
· To determine if insulin resistance in cells is the cause of hyperglycemia (high blood sugar)
· To determine if insulin supplementation is necessary
· To determine the presence of insulin-producing tumors (insulinomas) in the beta cells of the pancreas
What does Insulin-F Measure?
Carbohydrates consumed in the diet are digested and converted into the simple sugar, glucose. Glucose is absorbed by the cells for the production of energy, or stored in other forms like fats. Insulin is the hormone responsible for the uptake of glucose by the cells from blood for utilization and storage. It thus helps to maintain blood glucose levels within a normal range. Insulin also plays an essential role in the metabolism of lipids.
Levels of blood glucose and levels of insulin in blood maintain a balance with each other. A rise in blood sugar stimulates insulin production by the pancreas. This causes insulin levels to rise in blood. Insulin stimulates the uptake of glucose by cells, leading to a fall in blood glucose, and insulin levels in turn. Disruptions in this mechanism due to low insulin production by pancreas or inability of cells to respond to insulin (insulin resistance) cause a rise in blood sugar levels or hyperglycemia. Hyperglycemia is associated with diabetes. Diabetes Type 1 is an inherited condition where insulin is produced in insufficient quantities. Diabetes Type 2 occurs due to insufficient insulin production, or due to the development of insulin resistance. When cells are unable to respond to insulin, they cannot take up glucose from the blood effectively. The cells are deprived of glucose for energy, while glucose levels become high in the blood.
Insulin resistance increases with time. Increased glucose levels in blood stimulate the pancreas to produce excess insulin, leading to hyperinsulinemia (high insulin levels in the blood) along with hyperglycemia. Insulin resistance can also be seen in cases other than diabetes, such as prediabetes, polycystic ovarian syndrome (PCOS), pituitary or adrenal gland diseases, etc.
High insulin levels in the blood may also occur in patients suffering from tumors in the beta cells of pancreatic glands, or in cases of insulin overdose. Since excess insulin in these cases is not caused due to excess blood sugar levels, hyperinsulinemia in these cases can cause hypoglycemia (low blood sugar), leading to energy deprivation in all cells of the body.
Interpreting Insulin-F results
Normal range (Approx.): 2.0 - 25.0 uU/ml
Fasting Insulin Test is usually ordered with Fasting glucose test and the results interpreted as follows:
Fasting insulin level
Fasting glucose level
Normal or slightly high
Insufficient insulin production, e.g., diabetes
Normal or high
Hypoglycemia due to over secretion of insulin