Interleukin-6 Levels are not Increased in Women with Postpartum Thyroid Dysfunction

Postpartum thyroid dysfunction (PPTD) is an autoimmune-mediated thyroid destructive process. Human interleukin-6 (IL-6) is a cytokine found to be increased in subacute thyroiditis, amiodarone-induced thyrotoxicosis, Graves' disease, and other thyroid destructive processes. We report serum IL-6 levels in PPTD in two independent studies. New York Study: In a previous prospective study we demonstrated that PPTD occurred in 25% (7/28) of women with type 1 diabetes mellitus. IL-6 determinations were made on the frozen serum samples of these 28 women during each trimester of their pregnancy and at 1.5, 3, 6, 9, and 12 months postpartum. IL-6 levels were found to be similar in women with PPTD compared with women without PPTD (mean 3.06 ± 2.25 vs. 2.51 ± 2.21 pg/mL; p = 0.15). No difference in IL-6 levels was found between the pre- and the postpartum periods (mean 2.67 ± 1.82 vs. 3.04 ± 2.44 pg/mL; p = 0.30) in all 28 women. Cardiff Study: Serum IL-6 levels were measured on frozen serum samples of 30 women with PPTD. IL-6 levels were below the detection limit (25 fmol/L or 0.65 pg/mL) in 94 (67%) of these samples. No significant difference in the mean serum IL-6 levels were found between any time points in the study. There was no correlation between serum IL-6 levels, thyroid peroxidase (TPO)- antibodies and serum thyrotropin (TSH) levels at any time point. IL-6 levels during pregnancy or postpartum were not found to be significantly different in women with PPTD compared with women without PPTD.