Interactions between growth hormone and the thyroid gland -- with special reference to biochemical diagnosis

The diagnosis of pituitary disorders is difficult because several hormone systems are involved. The clinical presentation is often vague and slowly progressing, and clinicians therefore have to rely very much on correct biochemical measurements. This is also associated with difficulties since the pituitary hormones interact, the binding proteins are influenced by the other axes and a variety of other effects, and finally the hormone measurements in serum are not totally adequate Several studies have investigated the interaction between the thyroid and growth hormone axes with very variable results. The present review is focussing on the aspects related to clinical decision making based on biochemical assessments. Because of the strong and sometimes unpredictable interrelations between the hypothalamo-pituitary thyroid and the hypothalamo-GH-IGF axes, and the many pitfalls in the measurement of peripheral hormones and interpretation of stimulation tests, clinicians and clinical biochemists should collaborate closely. Only then can the diagnostic accuracy and the management of patients with both growth hormone and thyroid disorders be improved.