Abstract Body: Introduction: Thyroid hormones are of fundamental significance for brain function and showed neuroprotective effects in acute ischemic stroke (AIS) in animal models. Human studies associated the decline of free triiodothyronine (fT3) after AIS with its severity, but whether thyroid function correlates with more severe strokes during hyperacute presentation remains unclear. In this study, we evaluated thyroid hormones < 24 hours after the patient's last known well and correlated them with stroke severity.

Methods: We retrospectively collected baseline demographical and clinical data of 1379 patients who presented as stroke alerts within 24 hours of symptoms to our institution and were confirmed to have AIS between 2016 and 2024 by brain magnetic resonance imaging (MRI). Baseline demographics were reported by descriptive characteristics. We used the National Institute of Health Stroke Scale (NIHSS) to determine stroke severity. Thyroid-stimulating hormone (TSH), fT3, and free thyroxine (fT4) levels were tested at the time of presentation and correlated with the NIHSS score using the Spearman correlation coefficient. We used the Bonferroni method for multiple comparisons. Alpha was set at 0.05.

Results: The mean age for our cohort was 72.78 years ± 14.44, 49% were females, 74.33% of the patients were Caucasian and 16.17% were African American. In 2.9% of patients, the NIHSS was 0, 18.64% had an NIHSS of 1-4, 45.83% had an NIHSS of 5-15, 15.3% had an NIHSS of 16-20, and 13.13% had an NIHSS of 21- 42. The mean fT3 level was 2.65 pg/ml ± 1.00, that of the fT4 level was 1.26 ng/dl ± 0.33, and that of TSH was 2.97 uIU/ml ± 7.49. We found a negative correlation between hyperacute NIHSS score and fT3 (p<0.0001) and fT4 (p=0.0391). After Bonferroni correction, only lower fT3 significantly correlated with higher NIHSS (p<0.0001). We found no correlation between TSH and NIHSS.

Conclusion: Lower fT3 levels during hyperacute stroke presentation are associated with more severe strokes. If proven in large-scale studies, supplementation of triiodothyronine during hyperacute presentation may be neuroprotective and improve stroke outcomes.