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Glucagon Test

INDICATION

Assessment of growth hormone and ACTH/cortisol reserve especially when insulin-induced hypoglycaemia is contra indicated.

CONTRAINDICATIONS

Phaeochromocytoma or insulinoma (may provoke an attack)
Starvation >48 hours or glycogen storage diseases (inability to mobilise glycogen may result in hypoglycaemia)
Severe hypocortisolaemia (0900h level <55 nmol/l)
Thyroxine deficiency may reduce GH and cortisol response.

SIDE EFFECTS

Nausea is common (30%) and patients may rarely vomit.

PREPARATION

Fasting from midnight. The patient does not need to be continually observed as hypoglycaemia is not provoked.
Calculate glucagon dose:
adults: 1 mg, 1.5mg if > 90kg
children: 15 mcg/kg
6 fluoride bottles (grey top Vacutainers)
6 plain tubes (red top Vacutainers)

METHOD

  1. Insert an indwelling cannula.
  2. Take basal samples for glucose, cortisol and GH.
  3. Give the glucagon i.m. (the deltoid may be a suitable site).
  4. Take further samples at 90, 120, 150 and 180 minutes.

INTERPRETATION

Adequate cortisol response is defined as a rise of greater than 170 nmol/l to above 550nmol/l. Adequate GH response is a rise to a value greater than 20 mU/l.

SENSITIVITY AND SPECIFICITY

This test is probably slightly less reliable test of somatotroph and corticotroph function than the ITT. It is an excellent alternative in patients who can not tolerate hypoglycaemia because of epilepsy, ischaemic heart disease or hypopituitarism. The false negative rate for cortisol response is 30% (but only 8% of normals will not show either a peak value of 550nmol or a rise of 170nmol/l). Only 4-8 % of normals will not show an adequate rise in GH: this is usually in patients over 50.

REFERENCES

Rao R.H. et al., Metabolism 36, 658-663 (1987).