In the neonate dynamic testing should not be undertaken without suitable indwelling lines, and under the advice of a paediatric endocrinologist. For pituitary function testing, or corticotrophin-releasing hormone (CRH) test, this means an arterial line for sampling. A short Synacthen test can usually be performed without an arterial line.

Anterior pituitary function tests

• Measurement of random free thyroxine (fT4) and thyroid-stimulating hormone (TSH, after the initial postnatal surge in the first 2 days of life) provides information about pituitary and thyroid function.

• Baseline gonadotrophin levels (leuteinizing hormone, LH; follicle stimulation hormone, FSH) can also be informative, as they should be relatively high in the newborn period.

• Measurement of cortisol and growth hormone (GH) at the time of hypoglycaemia can be helpful, but, unlike older infants and children, the normal neonate may produce a good GH response to hypoglycaemia, but a poor cortisol response.

• Measurement of several (at least 3) random cortisol levels is useful, as cortisol is released in a pulsatile manner and may be low (e.g. 50 nmol/L) in normal infants if measured at the nadir. Timing is not important as diurnal variation does not appear for 8–12 weeks. All samples could be on the same day (and therefore the results could be reported together).

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