Purpose: Inflammation plays a critical role in the progression of COVID-19. Nonthyroidal illness syndrome (NTIS) has been increasingly recognized in affected patients. We aim to evaluate the correlation of thyroid hormones with markers of inflammation and association with disease outcome in hospitalized patients with COVID-19, and in two profiles of NTIS (low T3-normal/low FT4 vs. low T3-high FT4).

Methods: consecutive patients admitted to a nonintensive care unit for COVID-19 were recruited. Infection was mild in 22%, moderate in 27.1% and severe in 50.8%; 7.41% died. T4, T3, FT4, FT3, and their ratios (T3/T4, FT3/FT4) were correlated with albumin, ferritin, fibrinogen, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), lactate dehydrogenase (LDH), and D-dimer.

Results: Fifty five patients (50.9% men, median age 56 years) were included. Albumin correlated positively with T3 and hormones ratios, but negatively with FT4. T3, FT3, T3/T4, and FT3/FT4 correlated inversely with ferritin, fibrinogen, ESR, CRP, LDH, and D-dimer. FT4 showed direct correlation with fibrinogen and ESR. T3/T4 was lower in severe compared to mild/moderate disease [7.5 (4.5-15.5) vs. 9.2 (5.8-18.1); p = 0.04], and lower in patients who died than in those discharged [5 (4.53-5.6) vs. 8.1 (4.7-18.1); p = 0.03]. A low T3/high FT4 profile was associated with lower albumin, higher ferritin, and severity.

Conclusion: In this cohort, thyroid hormones correlated with inflammation and outcome. T3 and T3/T4 correlated inversely with inflammatory markers; a low T3/T4 ratio was associated with severity and poor prognosis. Patients with low T3 but high FT4 had higher ferritin, lower albumin, and more severe disease at presentation.