LAUSR

demic this is certainly worth consideration, however, rigorous evidence linking the two remains lacking. The diagnosis of methemoglobinemia is seldom thought of given its rarity, and thus may remain underdiagnosed during the COVID-19 pandemic. The typical presentation consists of abrupt symptoms of tissue hypoxia following exposure to an oxidizing substance. Notably, as this is a condition of increased heme-oxygen avidity rather than hypoxemia, dissolved oxygen levels on blood gas may be normal in spite of clinical evidence of hypoxia and decreased readings on pulse oximetry. A high index of suspicion is thus required and diagnosis is most often made on co-oximetry or specific blood Met-Hb assay. The severity of symptoms usually correlates with Met-Hb level, although patients with concurrent respiratory compromise (as those in this series) may become symptomatic at lower levels [4]. Treatment consists of discontinuation of the offending drug, and use of reduction agents such as methylene blue and/or ascorbic acid [2]. Refractory instances of methemoglobinemia may benefit from red-cell exchange (as demonstrated in case 2). Importantly, methylene blue is to be avoided among patients with G6PD deficiency, as demonstrated in case 3 wherein it worsened Coombs negative hemolysis in a G6PD deficient patient. Notably, this patient had some evidence of hemolysis even before receiving methylene blue, and it is unclear whether this may have been related to hydroxychloroquine (as he was on no other potentially oxidizing medications) or COVID-19 itself (although such a complication has not been well-described to date). The other patients in this series were not G6PD deficient (both were tested).