2013 年 40 巻 4 号 p. 468-475
Subclinical hypothyroidism (SHT) is defined as an asymptomatic state associated with normal serum FT4 and a slightly elevated serum TSH concentration. Patients with SHT have a high rate of progression to clinically overt hypothyroidism (OHT), and in addition, SHT is thought to be a risk factor for atherosclerosis and coronary heart disease. The aim of this study was to identify SHT patients and refer them to a thyroid specialist for treatment and management. We retrospectively studied 1168 subjects (324 males and 844 females) who received health check-ups including thyroid function tests in our Health Service Association Clinic over a period of three years and eleven months. Sixty subjects (5.1%) were diagnosed as SHT. The TSH/FT4 ratio (SHT index) was found to be helpful for diagnosing SHT. The main causes of SHT were Hashimoto's thyroiditis, excess dietary iodine intake. L-thyroxine replacement therapy was recommended for patients with a TSH greater than 10 μU/mL. For patients with very mild SHT who are pregnant or anticipate becoming pregnant, L-thyroxine therapy should be started. We devised a flowchart for the diagnosis and management of SHT.