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Pituitary Function Tests for Children

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. However, a prolonged test of GH secretion with multiple blood samples is an invasive procedure and in order to reduce the possible need for repeat investigation, it has been tradition to include the use of TRH and GnRH. Recent data suggests that additional stimulation with TRH and GnRH does not give any information that would not have been given by baseline measurements of gonadotropins, sex hormones, TSH and thyroxine.

Our practice is to use the glucagon test for evaluation of growth hormone and cortisol secretion, and to include TRH or GnRH only if there is a specific indication for these tests.

Contra-indications

see individual tests

Principle

see individual tests

Side effects

There is a greater risk of hypoglycaemia in children as they have smaller reserves of fat and carbohydrate and therefore, contingency plans must be available for its development. Most subjects given glucagon experience nausea and may vomit.

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 at least 4 hours after any food and drink.

Requirements

The following equipment should be immediately available: see protocol for emergency treatment of hypoglycaemia during ITT/glucagon test

  1. liquid drink (squash/milk), food (toast/biscuits)
  2. glucose powder, strong oral glucose solution (as for diabetics)
  3. 10% dextrose (500 mL) and iv giving set
  4. Glucose test strips and lancets etc
  5. hydrocortisone 100 mg for iv use
  6. 7 plain tubes
  7. an intravenous cannula

Drug administration: Glucagon 15 microgm/kg by im injection, maximum 1 mg.

Procedure

time 0 min

take 5 mL blood for fT4, TSH, LH, FSH, prolactin, GH, ACTH, IGF-1, cortisol & testosterone or oestradiol
immediately give glucagon intramuscularly

time 30 min

take 3 mL blood for cortisol & GH

time 60 min

take 3 mL blood for cortisol & GH

time 90 min

take 3 mL blood for cortisol & GH

time 120 min

take 3 mL blood for cortisol & GH

time 150 min

take 3 mL blood for cortisol & GH

time 180 min

take 3 mL blood for cortisol & GH

Interpretation

see for Glucagon test

Reference

  • Burke CW. The pituitary megatest: outdated? Clin Endocrinol (Oxf) 1992;36:133-134.
  • Westwood M, McLellan AC, Butler GE, Barth JH. TRH and LHRH stimulation tests in children with short stature? A retrospective analysis of one hundred and twenty six cases. Clin Endocrinol 2000;52:727-733.

Julian H Barth
17 Oct 2011

  

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