Negative association between free triiodothyronine level and international normalized ratio in euthyroid subjects with acute myocardial infarction.

AIM: To investigate the relationship between free triiodothyronine (FT3) and the international normalized ratio (the ratio of the prothrombin time of a patient to the normal sample, INR) in Chinese euthyroid subjects with acute ST-segment elevation myocardial infarction (STEMI). METHODS: A total of 231 consecutive patients (177 males, 54 females) with STEMI were enrolled. Anthropometric and laboratory measurements, including heart rate, respiratory rate, blood pressure, body temperature, platelet count, INR, prothrombin time, activated partial thromboplastin time, FT3, free thyroxine (FT4), and thyroid-stimulating hormone, were collected from all the patients. The levels of FT3 and FT4 were measured with a full-automatic immune analyzer. The INR was determined using a coagulation analyzer. RESULTS: Patients were classified into 4 groups according to their quartile FT3 and FT4 levels: 0.40-3.09 (n=52), 3.10-3.69 (n=56), 3.70-4.29 (n=64) and 4.30-7.10 (n=59) for FT3; 4.9-14.8 (n=57), 14.9-16.8 (n=58), 16.9-18.7 (n=57) and 18.8-29.0 (n=59) for FT4. Subjects with a high FT3 level had significantly lower values of INR than those with a low FT3 level (P=0.01). Multiple linear regression analysis revealed decreased serum FT3 as an independent risk factor for elevated INR values (ß=-0.139, P=0.025). The value of INR was similar among the 4 groups according to the quartile FT4 levels (P=0.36). CONCLUSION: Free triiodothyronine was negatively associated with INR in the patients with acute STEMI and normal thyroid function.