Plasma levels of NT-pro-brain natriuretic peptide in patients with overt and subclinical hyperthyroidism and hypothyroidism.

Background: Several studies have assessed natriuretic peptides in patients with thyroid disorders, and these studies have provided contrasting results. This difference may be partially explained by the presence of concomitant disorders of the cardiovascular system in participants.

Material And Methods: The study included 101 patients free of any cardiovascular disorder, who, on the basis of plasma levels of TSH and thyroid hormones, were divided into patients with overt hyperthyroidism, patients with subclinical hyperthyroidism, patients with overt hypothyroidism, patients with subclinical hypothyroidism, and control subjects with normal thyroid profile. Hyperthyroidism was induced either by nodular thyroid disease or by Graves' disease, while hypothyroidism was secondary to autoimmune thyroiditis or surgery.

Results: Compared to control subjects, hyperthyroid patients were characterised by higher plasma levels of NT-pro-BNP. This increase was particularly pronounced in cases of overt disease. On the other hand, neither clinical nor subclinical hypothyroidism was associated with any significant changes in this peptide. Plasma levels of NT-pro-BNP did not differ between patients with Graves' disease and toxic nodular goitre nor between patients with autoimmune hypothyroidism and hypothyroidism secondary to thyroidectomy. Only L-thyroxine substitutions, but not hyperthyroidism treatment, caused changes in plasma concentration of NT-pro-BNP.

Conclusions: Hyperthyroidism and hypothyroidism induce changes of the plasma concentration of NT-pro-BNP. Although both exogenous L-thyroxine and antithyroid drugs restored thyroid function, only the former drug changed plasma NT-pro-BNP content. The thyrometabolic state of a patient should always be taken into consideration when NT-pro-BNP is assessed as a marker of cardiac dysfunction.