Growth Hormone Suppression Test (GTT for Acromegaly)

Name
Growth Hormone Suppression Test (Glucose Tolerance Test for Acromegaly)
Tube Type(s)
Fluoride Oxalate (Grey Top) and
Serum (Gold Top)
Clinical Indication
Clinical suspicion of acromegaly or gigantism
Availability
Mon-Fri
Target turnaround time
1 working day
Special requirements & notes
Patient is advised to fast for 10-12 hours prior to the test. Small quantities of water are permissible.
Prepare a solution of glucose to drink – adults are given a 75g anhydrous solution (1.75g/kg body weight if this is being performed on a child). A pre-prepared solution may be available from pharmacy for this purpose.
Procedure
The patient should remain at rest throughout the duration of the test.
Collect a basal sample for growth hormone (gold top) and glucose (grey top)
Ensure the patient drinks the solution within 5 minutes.
Take paired samples (1 gold top, 1 grey top) at 30 minutes, 60 minutes, 90 minutes and 120 minutes after the glucose drink has been consumed.
Send all samples together to the laboratory with one request form for the series. Please indicate the time of sampling on each bottle e.g. 0/30/60/90/120
Clinical Report
Reported as a series of results in conjunction with glucose results. Normal response is to suppress GH production during the test.
Fasting GH may be normal in 8% of acromegalic subjections, but GH does not suppress to undetectable values during the test.
Volume required
5 samples each (4ml) of gold top and grey top – 10 samples in total.
If delayed transport to lab, store:
N/A
Factors affecting result interpretation
Contraindicated in patients with diabetes
GH may fail to suppress due to chronic renal failure, liver failure, active hepatitis, anorexia nervosa, malnutrition, hyperthyroidism, diabetes and adolescence.
Pathology discipline
Biochemistry
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Last updated: July 24, 2019