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Adapted from the Thyroid Testing Guidelines for Alberta Physicians - April 1992.
Thyroid stimulating hormone (TSH) is the initial test for the diagnosis of primary hyperthyroidism and hypothyroidism. The measurement of TSH levels is the most sensitive and specific test for thyroid dysfunction. The new generation of sensitive immunoradiometric TSH assays can reliably detect a concentration as low as 0.01 mU/L. Reference values range between 0.15 mU/L and 6 mU/L, but some variations are possible in different laboratories. Sensitivity and specificity of TSH is in excess of 90 percent in detecting thyroid disease (Caldwell, 1985).
The above recommendations are systematically developed statements to assist practitioner decisions about appropriate laboratory testing for specific medical conditions.
The Canadian Task Force on the Periodic Health Examination (1994) have reported that the prevalence rates of hyperthyroidism are 1.9 to 2.7 percent. The U.S. Preventive Services Task Force (1989) estimate that between 2 and 3 percent of the U.S. population have either hypothyroidism or hyperthyroidism. The annual incidence rate of overt hyperthyroidism has been estimated to be two to three per 1,000 women. The Thyroid Foundation of Canada estimates that thyroid disorders affect one in twenty Canadians and that most thyroid disorders are 5 - 7 times more common in women.
The prevalence of hypothyroidism is three times higher among women than men. The prevalence in an unselected community population of young, middle aged and elderly individuals is about 1.4 percent and the estimated annual incidence rate is one to two per 1,000 women. Surveys of geriatric populations have yielded estimated prevalence rates for overt hypothyroidism of 0.2 percent to 3 percent (Canadian Task Force on the Periodic Health Examination, 1994). The presentation of symptoms in the elderly may be atypical or absent (Singer et al, 1995; U.S. Preventive Services Task Force, 1989). The reported prevalence of subclinical hypothyroidism ranges from 0.9 percent to 5.2 percent in the adult population and from 2.6 percent to 20 percent in the elderly population.
Patients with thyrotoxicosis usually have TSH values less than 0.1 mU/L.
Benign Goitre or Nodules