MON-619 The Direct Stimulatory Effect of Thyroid Hormone Against Plasma Brain Natriuretic Peptide in Health Check-Up Participants: Cross-Sectional and Longitudinal Studies

Background: Circulating levels of thyroid hormone (TH) and TSH may not always reflect TH activity in specific peripheral tissues. Although the heart is one of the major target organs for TH, the tissue-specific circulating markers of TH activity have not been characterized. Therefore, we investigated the independent effects of TH status on plasma brain natriuretic peptide (BNP) concentrations in a large number of health check-up participants. Methods: We retrospectively analyzed data from participants who visited our hospital for health check-ups between July 2008 and March 2017. Among 20,403 participants, 12,409 revisited periodically. Participants were included in the cross-sectional study population if measurements of their concurrent TSH, free T4, body mass index, systolic blood pressure, hemoglobin, and estimated glomerular filtration rate were available at the initial visit. Longitudinal analysis was performed if the concurrent results for the participants were consecutively available. Exclusion criteria were abnormal electrocardiogram and/or a history of cardiac disease. Results: In the cross-sectional study (n = 2,807), multivariate analyses demonstrated a significant elevation in BNP (logarithmically converted) in overt thyrotoxicosis (OT; n = 21) compared with euthyroidism (n = 2,629), but not in subclinical thyrotoxicosis (SCT; n = 53), subclinical hypothyroidism (SCH; n = 97), or overt hypothyroidism (OH; n = 7). However, the standardized partial regression coefficient for thyroid function category against BNP was the lowest (β = 0.048, p = 0.006) among several other independent variables. After participants with OT or OH were excluded because of the small group size, the longitudinal study (n = 990) demonstrated no significant differences in the annualized rate of change in BNP among SCT (n = 4), SCH (n = 963), and euthyroidism (n = 23). Conclusions: The direct stimulatory effects of TH on BNP were only confirmed for OT. Our study suggests that plasma BNP concentrations are not sufficiently sensitive to evaluate TH activity in the heart. Physicians should consider multiple independent contributing factors other than thyroid dysfunction when interpreting BNP data in patients with thyroid disorders.