The growth hormone suppression test determines whether growth hormone (GH) production is suppressed by high blood sugar.
How the Test is Performed
At least three blood samples are taken.
The test is done in the following way:
- The first blood sample is collected between 6 a.m. and 8 a.m before you eat or drink anything.
- You then drink a solution containing glucose (sugar). You may be told to drink slowly to avoid becoming nauseated. But you must drink the solution within 5 minutes to ensure the test result is accurate.
- The next blood samples are usually collected for 1 to 2 hours after you finish drinking the glucose solution. Sometimes they are taken every 30 or 60 minutes.
- Each sample is sent to the laboratory right away. The lab measures the glucose and GH levels in each sample.
How to Prepare for the Test
Do not eat anything and limit physical activity for 10 to 12 hours before the test.
You may also be told to stop taking medicines that can affect the test results. These medicines include glucocorticoids such as prednisone, hydrocortisone, or dexamethasone. Check with your health care provider before stopping any medications.
You will be asked to relax for at least 90 minutes before the test. This is because exercise or increased activity can change GH levels.
If your child is to have this test done, it may be helpful to explain how the test will feel and even demonstrate on a doll. The more familiar your child is with what will happen and why, the less anxiety the child will feel.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.
Normal test results show a GH level of less than 1 nanogram per milliliter (ng/mL). In children, GH level may be increased due to reactive hypoglycemia.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
If the GH levels are not changed and stay high during the suppression test, the doctor will suspect gigantism or acromegaly. You may need to be retested to confirm the test results.
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight, but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
GH suppression test; Glucose loading test
Guber HA, Farag AF. Evaluation of endocrine function. In McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 24.
Melmed S, Kleinberg D, Ho K. Pituitary physiology and diagnostic evaluation. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, eds. Williams Textbook of Endocrinology. 12th ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 8.
Update Date 12/4/2013
Updated by: Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.