Cardiac troponin T is not increased in patients with hypothyroidism

Patients with hypothyroidism often have increased creatine kinase (CK) levels. It is possible that there is increased production of CK, but other mechanisms, such as an increased cell membrane permeability or decreased enzyme clearance were also proposed. Recently, troponins T and I have been extensively studied because of their cardiac specificity. Cardiac troponins are sensitive and specific markers of cardiac injury. The objective of the study was to measure cardiac troponin T (cTnT) levels in patients with hypothyroidism. Twenty-five patients with primary hypothyroidism were evaluated (thyroid-stimulating hormone (TSH) >30 mU/L and low FT₄). In all patients thyrotropin (TSH), free thyroxine (FT₄), CK, CK-MB and cTnT were measured.There were 3 men and 22 women with a mean age of 47.5 ± 12.4 years. TSH levels ranged from 31 to 75 mIU/L and mean FT₄ levels were 4.5 ± 1.9 pmol/L. CK was normal in 11 patients and increased in 14. CK levels ranged between 86 and 1221 U/L (normal levels <170 in women, <195 in men) with a mean of 322 U/L ± 279. CK-MB was increased in 4 patients (16%) and normal in 21. All 25 patients had normal cTnT levels, < 0.01 ng/mL (normal levels 0–0.1 μg/L). Increase in CK and its MB fraction are common in patients with hypothyroidism but cTnT levels are not, even in patients with increased CK-MB. Therefore, cTnT is a reliable marker of cardiac injury even in the hypothyroid patient.