SAT-405 TSH testing patterns for patients with type 2 diabetes and hypothyroidism after GLP-1 RA initiation in a target trial setting

Abstract Disclosure: N.M. Singh Ospina: None. Y. Chen: None. F. Du: None. J.P. Brito: None. H. Shao: None. Q. Liu: None. R.G. McCoy: None. T. Jiao: None. Background: The levothyroxine dose for patients with hypothyroidism is highly correlated with weight. In patients with hypothyroidism, TSH measurements are used to assess the adequacy of levothyroxine dosing.Since type 2 diabetes (T2D) and obesity are two common comorbidities for patients with hypothyroidism, and the significant weight loss associated with Glucagon-Like Peptide-1 Receptor Agonists (GLP-1 RAs) therapy, the initiation of GLP-1 RA on levothyroxine users may significant increase the need for levothyroxine dose reduction potentially requiring additional TSH tests to assure control. Objectives: To evaluate the timing and frequency of TSH testing within one year of initiation of GLP-1, or sodium-glucose co-transporter 2 (SGLT-2) inhibitors, in patients with T2D on levothyroxine treatment. Methods: We identified a cohort of T2D patients using 15% of Medicare fee-for-service claims data from 2005 to 2020. Cohort entry was defined by the initiation of GLP-1 or SGLT2. Patients needed to continuously receive the same dose of levothyroxine for >6 months and have at least 1 TSH measurement before the index date. We excluded patients with hyperthyroidism, thyroid cancer, end-stage renal disease, HIV/AIDs, organ transplant, or who received medications that affect thyroid levels before the index date. The primary outcome was the timing and frequency of TSH testing within one year after GLP-1 RA initiation. Demographics, comorbidities, and medication use were balanced using 1:1 propensity score matching based on the index date. Results: After matching, no significant demographic differences were observed among the 2,107 patients in GLP-1 RA and SGLT-2 groups, respectively. Overall, 32.1%, 32.3%, and 35.6% were aged 65-70, 70-74, and over 75, with 69.3% female and 87.9% white. In the year before the index date, the average number of TSH tests was higher in the GLP-1 RA (1.16 ± 1.27) compared to the SGLT2 (1.07 ± 1.18, p-value: 0.001). In the year after the index date, the average number of TSH tests declined to 0.93 ± 1.18 for GLP-1 and 0.89 ± 1.13 for SGLT2 (p-value: 0.03). Most patients (48.6 vs. 49.5%) had no TSH tests, 41.3 vs. 40.6% had 1-2 tests, and 10.1 vs. 9.9% had more than 2 tests in the GLP-1 RA and SGLT-2 group, respectively. Fewer patients (32.3 vs. 33.6%) were tested within 0-6 months while the majority (67.7 vs. 66.5%) waited longer than 6 months. The relative risk of TSH testing between the GLP-1 RA group and the SGLT2 group was 1.03 (95% CI: 0.98 to 1.08) 1-year before the index date and 1.00 (95% CI: 0.94 to 1.06) 1-year after the index date. Conclusions: Despite the potential impact of GLP-1 RA on levothyroxine dosing, on average, half of patients did not receive a TSH test after treatment initiation. There were no significant differences in TSH testing patterns between GLP-1 and SGLT2 groups, with similar test frequencies and timing observed. Presentation: Saturday, July 12, 2025