This test measures the amount of insulin, the hormone that lets cells take in glucose. Glucose, a sugar that comes from food, is the body's main source of energy. Our bodies break down foods we eat into glucose and other nutrients, which are then absorbed into the bloodstream from the gastrointestinal tract.
Glucose levels in the blood rise after meals and trigger the pancreas to make insulin and release it into the blood. Insulin works like a key that opens the doors to cells and allows the glucose in. Without insulin, glucose can't get into the cells and it stays in the bloodstream.
For good health, the body must be able to keep insulin and glucose levels in balance. With too little insulin, blood sugar remains higher than normal (a condition known as hyperglycemia) and cells can't get the energy they need. With too much insulin, blood sugar decreases (hypoglycemia), causing symptoms such as sweating, trembling, lightheadedness, and in extreme cases, shock. The most common cause of abnormal fluctuations in blood sugar is diabetes.
Why It's Done
This test is often used to evaluate the cause of hypoglycemia (low blood sugar) or any other conditions related to abnormal insulin production. It's often used to diagnose and monitor insulin resistance, a condition in which the tissues become less sensitive to the effects of insulin, causing the pancreas to overcompensate and produce more insulin. Insulin resistance is common among obese people who may go on to develop type 2 diabetes and also in women with polycystic ovarian syndrome.
Insulin levels are very low — despite the presence of high blood sugar levels — in children who have type 1 diabetes.
Your doctor will let you know if any special preparations are needed for this test. Sometimes a child will need to avoid eating and drinking for 8 hours prior to the test; other times, doctors want to check levels at specified times, such as shortly after a meal.
It may help to have your child wear a T-shirt or short-sleeved shirt on the day of the test to make things faster and easier for the technician who will be drawing the blood.
A health professional will usually draw the blood from a vein after cleaning the skin surface with antiseptic, and then placing an elastic band (tourniquet) around the upper arm to apply pressure and cause the veins to swell with blood. A needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.
After the procedure, the elastic band is removed. Once the blood has been collected, the needle is removed and the area is covered with cotton or a bandage to stop the bleeding. Collecting blood for this test will only take a few minutes.
What to Expect
Collecting a blood sample is only temporarily uncomfortable and can feel like a quick pinprick. Afterward, there may be some mild bruising, which should go away in a day or so.
The blood sample will be processed by a machine. The results are commonly available within a few days.
The insulin test is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn. These include:
fainting or feeling lightheaded
hematoma (blood accumulating under the skin causing a lump or bruise)
pain associated with multiple punctures to locate a vein
Helping Your Child
Having a blood test is relatively painless. Still, many children are afraid of needles. Explaining the test in terms your child can understand might help ease some of the fear.
Allow your child to ask the technician any questions he or she might have. Tell your child to try to relax and stay still during the procedure, as tensing muscles and moving can make it harder and more painful to draw blood. It also may help for your child to look away when the needle is being inserted into the skin.
If You Have Questions
If you have questions about the insulin test, speak with your doctor. You also can talk to the technician before the procedure.