Stability of thyroid function in older adults: the Birmingham Elderly Thyroid Study.

Area of Science:

• Endocrinology
• Geriatric Medicine
• Clinical Chemistry

Background:

• Thyroid function tests (TFTs) are frequently requested globally.
• Current testing practices are inconsistent, potentially leading to suboptimal care and increased costs.
• The long-term behavior of thyroid function requires further understanding.

Purpose of the Study:

• To assess the stability of thyroid function over a five-year period.
• To identify factors that predict the development of overt thyroid dysfunction.

Main Methods:

• A longitudinal study followed 2936 participants from the Birmingham Elderly Thyroid Study (BETS 1).
• Participants with baseline euthyroid or subclinical thyroid function results were re-tested after approximately five years.
• Changes in thyroid-stimulating hormone (TSH), free thyroxine (FT4), and thyroid status were analyzed, with predictors of dysfunction progression modeled.

Main Results:

• Thyroid-stimulating hormone (TSH) and free thyroxine (FT4) showed significant stability over five years; 61% of participants had repeat TSH within 0.5 mIU/L of baseline.
• Individuals with subclinical thyroid dysfunction at baseline were significantly more likely to develop overt hypothyroidism (10-fold) and hyperthyroidism (16-fold).
• Predictors for overt hypothyroidism included amiodarone treatment (OR 92.1), new atrial fibrillation (OR 7.4), and renal disease (OR 4.8).

Conclusions:

• Thyroid function is highly stable over a five-year interval, suggesting that routine repeat testing may be unnecessary, particularly for euthyroid individuals with recent results.
• Reducing repeat TFTs in older populations is feasible without increasing risk and can lead to substantial cost savings.