Utility of Thyroid Stimulating Hormone (TSH) in Atrial Fibrillation

Atrial fibrillation (AF) has become increasingly common in the inpatient setting. Current practices in new onset AF include obtaining laboratory values such as thyroid stimulating hormone (TSH) with reflex thyroxine (T4). We aim to prove that such practices rarely change management and should be limited to patients with additional indicators of hyperthyroidism. From January 2015 to August 2021, a total of 59,470 patients that were 18 years and older were identified with an admission diagnosis of atrial fibrillation using the ICD-10 code I48.92. Patients were excluded if their sex or age were not identified and if they had a previous admission for atrial fibrillation. Out of the 54,968 patients admitted with AF, TSH was ordered in 7,444 (13.54%), free T4 was ordered in 2,669 (4.85%), and both in 2,285 (4.16%). Only 29 (0.013%) of the 2,285 patients who had orders for both TSH and T4 were found to have both low TSH and high T4, indicating an overt hyperthyroid state. Overall, of the 7,444 patients with TSH labs drawn, only 404 (5.43%) were discharged on methimazole or Propylthiouracil (PTU). While we recognize the importance of identifying modifiable risk factors, we propose that TSH levels should not be reflexively ordered during hospitalization for patients with new onset AF without further clinical suspicion of thyroid disease.