ABSTRACT
Background: Subclinical hypothyroidism(SCH) is a common biochemical abnormality which can be found in routine screening tests of thyroid function. We are increasingly faced with the question of whether its an indication for thyroxine replacement therapy. The effect of thyroxine replacement on lipid profile in SCH has aroused a great interest because of an association of overt hypothyroidism(OVH) with hyperlipidemia and increased risk of coronary artery disease. Method: We prospectively evaluated the changes in lipids and apoproteins before and after thyroxine replacement therapy in 23 patients with SCH and in 37 patients with OVH. We measured serum total cholesterol and triglyceride using autoanalyzer, high density lipoprotein(HDL) chole-sterol by dextran sulfate method, Apo A1 and Apo B by immunonephelometric assay. Results: Thyroxine replacement therapy significantly decreased total cholesterol, low density lipoprotein(LDL) cholesterol and apo B levels, but did not affect the level of triglyceride, HDL cholesterol or apo AI in patients with OVH. In SCH, thyroxine replacement therapy with the doses to normalize serum TSH concentrations also decreased significantly the level of cholesterol and LDL cholesterol albeit apo B levels did not change. Moreover, in most of patients with OVH (11 of 12) and in all of patients with SCH(5 of 5) who had had hyperchlesterolemia before treatment, thyroxine replament normalized their cholesterol and LDL cholesterol levels. Conclusion: In regard to the beneficial changes in blood lipid levels, patients with SCH should be treated, especially in cases who have other risk factors for the development of atherosclerosis. If thyroxine replacement only will reduce the incidence of coronary artery disease in SCH remains to be elucidated by long-term prospective studies.