3.2. Characteristics of the Included Studies
From the seven studies included in this review for the case of MetHb and COVID-19, two were cross-sectional studies [19,21] and five case reports [17,18,20,22,23]. The case descriptions reported findings of one single patient [17,20,22,23] or three patients [18]. Five studies were published in journals [17,18,20,21,22] and two on the preprint server medRxiv (medrxiv.org) [19,23].
For the case of the three studies concerning COHb and COVID-19, two were cross sectional studies [24,25] and one a case report [20]. Two of the studies were published in journals [20,25] and one on the preprint server Research Square (researchsquare.com) [24].