Association of the free triiodothyronine to thyroxine ratio with acute post-stroke cognitive impairment: a cross-sectional study

Objective Thyroid dysfunction is recognised as a modulator of cognitive outcomes in stroke survivors. The free triiodothyronine (FT3)/free thyroxine (FT4) ratio remains unexplored in post-stroke cognitive impairment (PSCI). This study aimed to investigate the association between the FT3/FT4 ratio and PSCI.Methods Five hundred and twenty-three patients with ischaemic stroke were enrolled. Cognitive function was assessed using the Mini-Mental State Examination (MMSE). Participants were stratified into PSCI (n = 272) and non-PSCI (n = 251) groups based on education-adjusted MMSE thresholds. Thyroid hormone levels were measured, and the FT3/FT4 ratio was categorised into tertiles.Results Patients with PSCI exhibited significantly higher FT4 (p < 0.001) and lower FT3 (p < 0.001) levels compared to non-PSCI patients, resulting in a reduced FT3/FT4 ratio (p < 0.001). Logistic regression revealed that the lowest tertile of the FT3/FT4 ratio was independently associated with PSCI (OR = 2.135, p = 0.002). The FT3/FT4 ratio demonstrated superior discriminative ability compared to FT3 (p = 0.047) or FT4 (p = 0.021) alone, as indicated by a larger area under the curve (AUC).Conclusions A reduced FT3/FT4 ratio is independently associated with PSCI in the acute phase of ischaemic stroke, identifying it as a potential risk marker for PSCI.