Endocrine Abstracts

Introduction: The relationship between thyroid function tests and lipid parameters is still under hot discussion. According to current recommendations thyroid stimulating hormone (TSH) levels should preferably be below 2.5 mIU/l in healthy women of childbearing age as well as in women on levothyroxine treatment.

Aim: To compare lipid levels and atherogenic indices in premenopausal euthyroid healthy women and women with autoimmune thyroiditis (AIT) on levothyroxyne replacement therapy according to TSH values and evaluate their association with thyroid function tests.

Patients and Methods: 56 women with AIT and 195 healthy premenopausal women aged 18–40 years were included in the study. Serum levels of TSH, free thyroxine (FT4), total cholesterol, HDL and triglycerides were measured; LDL values were calculated using Friedewald formula. Castelli risk index I (CRI) and II (CRII), atherogenic coefficient (AC) and atherogenic index of plasma (AIP) were calculated. All women were euthyroid with TSH levels between 0.4–4.2 mIU/l and FT4 levels within the reference range (7.86–14.40 pmol/l), not taking steroids, metformin, lipid lowering medications or estrogen containing drugs.

Results: 42.9% of the women with AIT had TSH ≥ 2.5 mIU/l compared to 28.7% of the healthy women (P = 0.052). FT4 levels in women on levothyroxine replacement were higher than in the healthy women in both groups according to TSH levels. No differences between lipid parameteres and atherogenic indicis were found in healthy women and those on levothyroxine with TSH < 2.5 mIU/l. In the group with TSH≥ 2.5 mIU/l healthy women hadelevated levels of total cholesterol more frequently than those with AIT (51.8% vs 20.8%, P = 0.013). In women with AIT TSH levels did not show any relation to the lipid parameteres, but there was a significant negative correlation between FT4 and total and LDL cholesterol (P < 0.01) and I1, I2 and AC (P < 0.05). In healthy women TSH was associated neither with lipid levels nor with atherogenic indicis. However FT4 showed significant negative correlation with HDL levels (P < 0.01) and positive with I1, I2, AC (P < 0.05).

Conclusion: Our results suggest that FT4 levels have different impact on lipid metabolism in healthy women and women with AIT. Whether this finding is associated with clinically significant increase in cardiovascular risk and whether intervention is reasonable remains a matter of further investigation.

Keywords: autoimmune thyroiditis, thyroid stimulating hormone, free thyroxine, lipid parameters, atherogenic indicis.