Assessment of the relationship between subclinical hypothyroidism and blood lipid profile: reliable or not?

The relationship between subclinical hypothyroidism (SCH) and blood lipid metabolism is controversial. This study is intended to evaluate the relationship between SCH and blood lipid profiles using well defined diagnostic criteria.

Data from 11,512 physical examinees in our hospital who had finished two tests with an interval of at least 3 months were analyzed, including 685 cases of SCH as stipulated in this study. In addition to common physical examination indicators, other parameters such as thyroid function indices and blood lipids were measured twice with an interval of at least 3 months. Subjects were diagnosed with SCH only when their levels of TT3, TT4, FT3 and FT4 were normal and TSH levels were increased on both tests, which meant these subjects were in a state of SCH for at least 3 months. The results of blood lipids for the second time were analyzed.

Statistically significant differences were found in age, sex, BMI, hemoglobin, total cholesterol (TC), low density lipoprotein (LDL-C), high density lipoprotein (HDL-C), and BFP between the SCH and control groups (P < 0.001). However, there were no statistically significant differences in age, sex, blood pressure, blood lipids, blood glucose or BMI between patients with mild SCH and those with severe SCH (P > 0.05). After balancing the age and sex ratio, no factors were confirmed to be statistically significant independent factors of SCH. None of the parameters showed statistically significant differences between patients with mild SCH and those with severe SCH (P > 0.05).

After defining rigorous criteria for the diagnosis of SCH, no definite association between SCH and TC, LDL-C or HDL-C was confirmed in this study. SCH may have no relationship to the most concerning blood lipid profile.