Diagnosing unsuspected hypopituitarism in adults from suggestive thyroid function test results

Area of Science:

• Endocrinology
• Clinical Biochemistry
• Public Health

Background:

• Hypopituitarism diagnosis often involves subnormal free T4 (fT4) or total T4 with normal or elevated thyroid-stimulating hormone (TSH).
• Previous studies estimated hypopituitarism incidence at 3.2 cases/100,000/year based on abnormal thyroid function tests (TFTs).

Purpose of the Study:

• To determine the incidence of unsuspected hypopituitarism through reflective testing of TFT samples in a Scottish population.
• To evaluate the utility of laboratory-based reflective testing for early hypopituitarism detection.

Main Methods:

• Prospective audit of TFT results over 15 months for a population of 200,000.
• Identification of individuals with specific TFT criteria (fT4 < 9 pmol/L, TSH < 10 mU/L) using a laboratory information system.
• Analysis of additional hormones including repeat fT4, total T3, testosterone, LH, FSH, prolactin, and cortisol on appropriate samples.

Main Results:

• 10 new cases of hypopituitarism were diagnosed in 266 adults from 73,650 TFT results, yielding an incidence of approximately 4 cases/100,000/year.
• Five cases showed abnormal pituitary imaging (tumors, empty sellae), three had normal imaging, and two were not scanned.
• Nine of the ten diagnosed patients are now attending endocrine clinics.

Conclusions:

• Reflective testing on TFT samples can diagnose a significant number of unsuspected hypopituitarism cases.
• Free T4 (fT4) analysis should be integral to frontline TFTs, as TSH alone is insufficient for identifying potential hypopituitarism.
• Laboratories are well-positioned to facilitate early hypopituitarism identification, potentially improving patient outcomes.