Diagnosis of pituitary hormone deficiency
| FSH, follicle stimulating hormone; GH, growth hormone; LH, luteinising hormone; TSH, thyroid stimulating hormone. |
| • Glucocorticoid deficiency: |
| Provided the patient has not taken exogenous glucocorticoids for at least 24 hours, a single plasma cortisol of <495 nmol/l measured one hour after a 250 µg intramuscular or intravenous bolus of adrenocorticotrophic hormone (ACTH, synacthen) indicates deficiency |
| • Thyroid hormone deficiency: |
| Free thyroxine (FT4) at or below the bottom of the normal range indicates deficiency: thyrotrophin values (TSH) are frequently within the “normal” range. A patient who is listless and gaining weight and whose FT4 and TSH are both near the lower limit of the normal ranges is likely to have secondary hypothyroidism and may benefit from a trial of thyroxine replacement |
| • Sex hormone deficiency: |
| Amenorrhoea in women and tiredness and loss of libido in men. Erectile function is often impaired and both sexes become infertile with suppressed or low normal concentrations of gonadotrophins (FSH and LH). In women, no confirmatory tests are usually necessary. In men, low circulating testosterone concentrations indicate deficiency |
| • Growth hormone deficiency: |
| The peak GH secretory response to a bolus of GH releasing hormone (1 µg/kg) given at the beginning of a 30 minute infusion of arginine (0.5 g/kg) is a safer and more potent GH secretogogue than insulin induced hypoglycaemia.11 Measured every 15 minutes for 2 hours from time zero, failure to reach 20 mU/l (in our practice) indicates deficiency |
| • Vasopressin deficiency: |
| Transient polyuria, nocturia, and thirst following pituitary surgery is usually sufficient to make the diagnosis of diabetes insipidus. Formal water deprivation testing is rarely required |