Random

Occasionally a random blood sample will detect an elevated GH level, particularly if the child is stressed or is fasted.

Such a result would exclude GH deficiency. However, the test is so unreliable that it is not recommended.

There as been a recent resurgance of interest in urinary GH measurements now that more sensitive GH assays are available. A 24 h or an overnight urine collection without preservatives is required. It is preferable to keep the urine stored at 4°C until the collection is completed. An ultrasensitive GH assay is required to detect the low levels associated with GH deficiency. The reliability of using urinary GH assays to screen short children for GH deficiency is currently being evaluated.

Insulin-like growth factor I (IGF-I) is GH-dependent and, as expected, the serum levels of this peptide are low in GH deficiency. Random measurements are too nonspecific for diagnostic use as levels are low in young children and are also affected by liver disease and hypothyroidism. Elevated GH and decreased IGF-I levels are characteristic of Laron’s dwarfism.

Exercise

This test should be performed using a bicycle ergometer to generate a standard amount of work which will vary according to the age and size of the child.

One should aim for a physical exertion between 150 and 300 kilopond. m/min equivalent to about 50 per cent maximal working capacity.

If a bicycle ergometer is not available, the following exercise test is sometimes useful to perform:

Interpretation: A GH level > 15 mU/l excludes GH deficiency. Lower values do not necessarily indicate GH deficiency. If necessary proceed to pharmacological tests. About 20 per cent of exercise-induced tests give false positive results for GH deficiency. Some protocols suggest priming the child with propanolol orally 0·5 mg/kg (maximum dose 40 mg) 1 hour before the test to enhance the GH response. This carries a risk of hypoglycaemia

Sleep

Ideally this test should be performed with EEG monitoring if available.

Insulin-induced Hypoglycaemia (Insulin Tolerance Test, ITT)

Stress resulting from hypoglycaemia is the stimulus for GH release, believed to be mediated via an α-adrenergic pathway. The dangers are obvious. Contra-indications to performing this test include a history of convulsions, previous hypoglycaemic episodes, and diabetes mellitus.

During an ITT, the following are measured—blood glucose, GH, cortisol and PRL.

Symptoms of hypoglycaemia usually occur 15–30 min after the insulin injection. If severe, collect an immediate blood sample for hormone analysis, then give i.v. dextrose. At the end of the test, give the child a glucose-containing drink and a meal. DO NOT allow home until observations are satisfactory.

Interpretation: The blood glucose should decrease by 50 per cent or more of the basal value (t = 0 min) and/or there should be symptoms and signs of hypoglycaemia—drowsiness, sweating, headache (occasionally nausea and vomiting). With adequate hypoglycaemia, peak GH levels < 7 mU/l indicate GH deficiency. This is excluded with peak GH levels > 15 mU/l. Levels between 7–15 mU/l may indicate partial GH deficiency, but this requires confirmation with a second, different test of GH secretion.

Arginine Stimulation

This has now largely replaced the...