Diagnosing unsuspected hypopituitarism in adults from suggestive thyroid function test results.
Preiss D., Todd L., Panarelli M.
BACKGROUND: The typical pattern of thyroid function tests (TFTs) associated with hypopituitarism consists of subnormal free T4 (fT4) or total T4 and normal or marginally elevated thyroid-stimulating hormone (TSH). A previous study calculated an incidence of hypopituitarism of 3.2 cases/100,000/year by following up abnormal TFTs. The aim of this study was to verify the incidence of unsuspected hypopituitarism diagnosed by reflective testing on such samples in a Scottish population. METHODS: Prospective audit of TFT results over 15 months. Individuals with suitable results (fT4 < 9 pmol/L, TSH < 10 mU/L) were identified by the laboratory information system at the Biochemistry Department, Glasgow Royal Infirmary, serving a population of 200,000. fT4 (repeat analysis following assay recalibration), total T3, testosterone (males), luteinizing hormone, follicle-stimulating hormone, prolactin and cortisol were analysed on appropriate samples. RESULTS: Three hundred and eleven suitable results from 266 adult individuals were identified from a total of 73,650 TFT results, leading to the diagnosis of 10 new cases (age range 28-90 years) of hypopituitarism (approximately 4 cases/100,000/year). Nine patients now attend endocrine clinics. Pituitary imaging was abnormal in five cases (2 large pituitary tumours, one macroadenoma, 2 empty sellae), normal in three cases and two patients were not scanned. CONCLUSIONS: A significant number of cases of unsuspected hypopituitarism can be diagnosed by reflective testing on appropriate samples. fT4 should be an integral part of frontline TFTs as TSH alone cannot assist in the identification of possible hypopituitarism. Laboratories are in an excellent position to assist in early identification of hypopituitarism, which may lead to improved outcomes in such patients.