Case finding and screening strategies for thyroid dysfunction

Abstract

Background: A case can be made for routine testing for thyroid dysfunction (TD) in women aged over 50 years once every 5 years when they present for medical care (case finding). This recommendation is based on: (i) the prevalence of TD, predominantly hypothyroidism, (ii) the insensitivity of standard clinical assessment in detecting even overt TD, (iii) the sensitivity of a single test, serum thyroid stimulating hormone (TSH), in identifying both over- and under-function, (iv) the probable adverse consequences of failure to recognize even mild TD, (v) the safety and effectiveness of treatment, and (vi) presumed lack of adverse effect from the testing program.

Methods: A normal serum TSH value has a high negative predictive value in ruling out primary TD; if TSH is abnormal, measurement of serum free thyroxine (T(4)) and further clinical assessment are both required to establish the degree of TD.

Results: Case finding identifies more "subclinical" or mild TD (abnormal TSH, normal T(4) and triiodothyronine (T(3))), than overt disease, but a major benefit of widespread testing is the earlier detection and treatment of unsuspected overt disease. There is now evidence that mild TD has adverse consequences and should not merely be regarded as a prognostic indicator, but there is still no consensus whether there is a causal relationship between mild thyroid failure and dyslipidemia.

Conclusions: A case can be made for treatment of both mild thyrotoxicosis and hypothyroidism, but the therapeutic decision is generally simpler for hypothyroidism.