Background and aim It is known that NT-proBNP levels increase in cardiac failure. However, NT-proBNP levels in different thyroid states are still unclear. We aimed to evaluate serum NT-proBNP levels in both hyperthyroid and hypothyroid patients without cardiac insufficiency.
Subjects and methods Thirty-six patients with hyperthyroidism (42·9 ± 16·7 years), 25 patients with hypothyroidism (35·4 ± 13·9 years) and 34 age-matched euthyroid subjects (41·4 ± 13·8 years) were included in the study. After anthropometric evaluations, body fat analyses were determined by bioelectrical impedance. Electrocardiography and echocardiography were used in cardiac evaluations. Serum NT-proBNP was measured by immunoassay.
Results Mean serum NT-proBNP levels in hyperthyroid patients were higher than in both control subjects (13·65 ± 13·02 vs. 6·50 ± 4·83 pmol/l, P = 0·002) and hypothyroid patients (13·65 ± 13·02 vs. 5·98 ± 5·08 pmol/l, P = 0·003). However, mean serum NT-proBNP levels in hypothyroid patients were not different from those in control subjects. There was a positive correlation between serum NT-proBNP and thyroid hormones (NT-proBNP and FT3: r = 0·324, P = 0·001; NT-proBNP and FT4: r = 0·269, P = 0·009, respectively). Serum NT-proBNP levels were positively correlated with left ventricle end-diastolic diameters (r = 0·232, P = 0·04), interventricular septum thickness (r = 0·315, P = 0·006), and negatively correlated with left ventricular ejection fraction (r = –0·238, P = 0·04).
Conclusions Serum NT-proBNP levels may increase in hyperthyroidism independently of cardiac insufficiency. Therefore, hyperthyroidism may lead to cardiac ultrastructural changes undetermined by conventional echocardiography and these changes may be responsible for elevation of NT-proBNP levels. In contrast to decreased thyroid hormones, excess thyroid hormones may have a more pronounced effect on serum NT-proBNP levels.