A crucial balance exists between oxidant and antioxidant mechanisms in the functional immune system. We aimed to evaluate the contributions of balance between these systems to coronavirus disease 2019 (COVID‐19), a devastating pandemic caused by viral infection.

We analyzed serum oxidant and antioxidant stress parameters according to the clinical and demographic characteristics of children and adults with COVID‐19 and compared them against the values of healthy controls. Serum native thiol (NT), total thiol (TT), disulfide, total antioxidant status, total oxidant status, and ischemia‐modified albumin levels were evaluated and compared between groups.

A total of 79 children and 74 adults were evaluated in the present study, including 46 children and 40 adults with COVID‐19, 33 healthy children, and 34 healthy adults. TT, NT, and disulfide levels were significantly lower in the adult COVID‐19 group than in all other groups (p = .001, p = .001, and p = .005, respectively). Additionally, TT and NT levels were significantly lower in both pediatric and adult COVID‐19 cases with severe disease course than mild/moderate course. TT and NT levels were identified as predictors for the diagnosis of the adult COVID‐19 cases and as independent predictors for disease severity in both children and adults with COVID‐19.

Parameters that reveal the oxidant and antioxidant capacity, including TT and NT, appear to be good candidates for the accurate prediction of the clinical course among patients with COVID‐19.