Clonidine GH stimulation Test

Indication

Pituitary function tests are often requested in the diagnostic evaluation of short children. The aim under these circumstances is to determine the status of the growth hormone (GH) axis. This test may be use simulatneously with other secretagogues eg synacthen and GnRH.

Contra-indications

None

Principle

Unknown

Side effects

There is a risk of drowsiness and hypotension that may last in children for several hours.

Preparation

Priming with sex steroids is recommended in prepubertal children who are over 10 years of age (either chronological or bone age). Prescribe stilboestrol 1mg 12 hourly for 48 hours prior to test.

This test must be performed fasting and in the morning (at least 4 hours after any food and drink - water is permitted).

Requirements

1. Clonidine for oral use
2. 7 plain tubes
3. an intravenous cannula

Drug administration: Clonidine150 microgm/m² orally.

Procedure

time 0 min	take 5 mL blood for TSH, LH, FSH, prolactin, GH, IGF-1, cortisol & testosterone or oestradiol immediately give glucagon intramuscularly
time 30 min	take 2 mL blood for GH
time 60 min	take 2 mL blood for GH
time 90 min	take 2 mL blood for GH
time 120 min	take 2 mL blood for GH
time 150 min	take 2 mL blood for GH
time 180 min	take 2 mL blood for GH

Interpretation

An adequate rise may be defined as GH > 7µg/L (20mU/L)

Reference

• Rahim A, Toogood AA, Shalet SM. The assessment of growth hormone status in normal young adult males using a variety of provocative agents. Clin Endocrinol 1996;45:557-562. 

Julian H Barth  22 Sept 2011