Laboratory diagnosis of multiple pituitary hormone deficiencies: issues with testing of the growth and thyroid axes

Clinical manifestations of hypopituitarism are variable and depend on the severity of hormone deficiency, creating a diagnostic challenge for diagnosis of the non-classical patient who may have a less severe growth hormone (GH) deficiency and only a suggestion of possible hypothyroidism. Laboratory tests contribute to the diagnostic process, but the tests for growth and thyroid dysfunction, two of the most common manifestations of multiple pituitary hormone deficiency, are some of the most problematic from a methodological perspective. Patients in the "grey zone" of diagnosis, for whom there is no distinct dividing line or gold standard diagnostic test, are the focus of this article. Issues relating to the use of laboratory tests involving GH, insulin-like growth factor-I, and free thyroxine in the diagnosis of GH and thyroid deficiency are reviewed. Assay harmonization initiatives are required before clinical research studies are performed to establish diagnostic thresholds for GH and thyroid hormone deficiencies.