Borderline hypothyroidism: epidemiological aspects in women aged 45-70 years

OBJECTIVE: The rationale for assaying thyroid stimulating hormone (TSH) as part of a systematic screening program for hypothyroidism requires a clearl y defined epidemiological basis. PATIENTS AND METHODS: Starting in 1997, we performed a prospective multicen tric study in eleven health centers to define the frequency of borderline h ypothyroidism in the female population aged 45-70 years and to ascertain th e associated clinical features and laboratory findings and the long-term co urse. TSH assays were performed in the participating laboratories using the same microparticulate sandwich immunoenzyme method on fresh serum with an IMX or an Axysm. Pertinent data were collected at regular check-ups. RESULTS: In the population of 4,403 women aged a mean 55.2 years (SD 6.9 yr ), 131 (3%) had borderline hypothyroidism defined as ISH between 4 and 12 m U/ml and FT4 > 8 ng/l. There was an association between borderline hypothyr oidism and age, hormone status, presence of minor electrocardiogram anomali es, lipid profile, and use of cardiovascular or lipid lowering drugs. Inver sely, few signs and symptoms usually suggestive of dysthyroidism were assoc iated with borderline hypothyroidism. Thirty-five women were given replacem ent therapy by their primary care physician. CONCLUSION: The low frequency of borderline hypothyroidism in our populatio n and the very limited nature of the clinical signs would not plead for sys tematic TSH assay in regular health check-ups, in agreement with recommenda tions presented elsewhere.