A cross-sectional retrospective study to identify indicators for initiating thyroid hormone replacement therapy in patients with subclinical hypothyroidism

Subclinical hypothyroidism (SCH) is defined by elevated serum thyroid stimulating hormone (TSH) levels and normal levels of total or free thyroxin. SCH is associated with increased risk of cardiovascular morbidity and mortality, but convenient risk indicators are lacking. We aimed to identify reliable indicators of cardiovascular risk for determining initiation of thyroid hormone replacement therapy in SCH patients. This is a cross-sectional retrospective study. Medical records of 412 consecutive healthy subjects with SCH who underwent routine health check-ups at National Taiwan University Hospital between January 1, 2009 and December 31, 2009 were reviewed. Demographic, physical and clinical data were collected, including waist circumference, body mass index, thyroid function tests, fasting blood glucose, glycohemoglobin (HbA1c), and lipid profiles. Subjects were divided into three groups by HbA1c level: <= 5.6%, 5.7%-6.4%, and >= 6.5%. National Cholesterol Education Program Adult Treatment Panel III (NCEP ATPIII) risk assessment was used to estimate cardiovascular risk. Group 3 had significantly higher fasting blood glucose (P < 0.001), postprandial glucose (P < 0.001), triglycerides (P < 0.001) and lower HDL-C (P = 0.039) than groups 1 and 2. HbA1c levels >5.7% are associated with cardiovascular risk in SCH patients. HbA1c is an objective, convenient parameter for determining initiation of thyroid hormone replacement therapy in SCH patients with higher cardiovascular risk. Further studies are needed to demonstrate HbA1c capability for predicting cardiovascular risk in SCH patients and whether T4 treatment can improve outcomes.