Factors of variation and reference values for TSH in 45-70 year old women

Thyroid stimulating hormone (TSH) was measured in a sample of 4,403 women, aged 45-70 years in 11 Centers for health screening, to define the interest of this biological indicator for screening subclinical hypothyroidism. The aim of this work was to describe clinical signs, symptoms and medical history linked to TSH variations, to estimate the distribution of this hormone in a general population and reference limits in a selected subgroup. All the participating laboratories used the same third-generation immunoassay on fresh samples. In the general sample population (age mean: 55.2 6.9 yrs), 1.1% presented hyperthyroidism (TSH<0.3 mU/l) and 0.4% had hypothyroidism (TSH>12 mU/l). In the sub-sample of 151 women (3.4%) with TSH between 4-12 mU/l, 131 had subclinical hypothyroidism (FT4>8 ng/l). The TSH mean was significantly lower (- 10 to - 23%) in women presenting a nodular goiter. Inversely, TSH was higher in women with muscle cramps, asthenia, recent weight gain, morning eyelid edema and abnormal electrocardiogram. The reference limits for percentiles 2.5 and 97.5 were 0.43 and 3.71 mU/l on 1 348 subjects after excluding women having one of these symptoms or taking any drug treatment.