OBJECTIVES

To investigate the incidence and determinants of spontaneous normalization of thyroid-stimulating hormone (TSH) levels in older adults with subclinical hypothyroidism.

DESIGN

Data were pooled from two randomized, double-blind, placebo-controlled trials investigating the effect of levothyroxine treatment in subclinical hypothyroidism. Since we were interested in spontaneous normalization, we only included the pre-trial screening populations and the in-trial placebo groups.

SETTING

Community-dwelling older adults (≥ 65 years) from the Netherlands, Switzerland, Ireland, and the United Kingdom.

PARTICIPANTS

The pre-trial population (N=2335) consisted of older adults with biochemical subclinical hypothyroidism, defined as an elevated TSH level (≥ 4.60 mIU/L) and a free thyroxine (fT4) level within the laboratory-specific reference range, identified from clinical laboratory and general practice databases. Individuals with persistent subclinical hypothyroidism, defined as at least two measurements of elevated TSH levels ≥ three months apart, were randomized to levothyroxine/placebo, of which the in-trial placebo group (N=361) was included in the present study.

INTERVENTIONS

No intervention for the pre-trial population. The in-trial placebo group received a randomized, double-blind, placebo treatment with mock titration during one year.

MAIN OUTCOME MEASURE

The incidence of normalization of TSH levels was assessed and associations between participant characteristics and TSH normalization were analyzed using logistic regression.

RESULTS

In the pre-trial phase, TSH levels spontaneously normalized in 60.8% of the older adults in a median follow-up of one year. In the in-trial phase, levels still normalized in 39.9% of older adults with persistent subclinical hypothyroidism.

CONCLUSIONS

Since TSH levels spontaneously normalized in a large proportion of older adults, the frequency of routine follow-up measurements for subclinical hypothyroidism may be reduced.