Growth Hormone Suppression Test for Acromegaly

Growth Hormone Suppression Test for Acromegaly

Purpose: Growth hormone (hGH) suppression by a glucose load is the classic screening test for acromegaly. In addition, the test may be used to monitor the progress of treatment.

Rationale: Growth hormone excess is the cause of acromegaly. Direct single growth hormone measurements are not diagnostic because hGH is secreted episodically and cleared rapidly, with a half-life of about 20 minutes. This secretory pattern produces peaks of hGH in serum measurements. Growth hormone is suppressed by glucose in the normal individual. Failure to suppress hGH is diagnostic of acromegaly when coupled with elevated IGF1 and clinical signs of excess growth hormone.

Procedure

  1. The patient should be fasting prior to the start of the test.
  2. Blood is drawn for a baseline serum hGH test.
  3. A drink containing 75 grams of glucose is administered.
  4. Samples for analysis are collected for serum hGH every 30 minutes for two hours at 30-, 60-, 90-, and 120-minute intervals after the glucose drink is ingested.
  5. Centrifuge the samples within one hour after the blood is drawn and label the specimens as: baseline, 30, 60, 90, and 120 minutes.

Orderable Profile. Growth Hormone, Five Specimens (038836) allows five hGH test results: the baseline and four suppression tests.

Interpretation: The diagnostic criterion for acromegaly is met if the hGH does not suppress below 1 ng/mL.1 The suppression test is reported to have a false-negative rate as high as 50%. The sensitivity of the test is reported to be improved at a cutoff of 0.4 ng/mL.2 The diagnosis includes clinical signs of growth hormone excess and elevated IGF1 levels.1

False-positive results with values that remain higher than 1 ng/mL after glucose administration may be observed in puberty and in patients with diabetes, liver disease, renal disease, or anorexia nervosa. Elevated IGF1 results may be observed during normal pregnancy.

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