2. Methods
The literature research was performed with MEDLINE (PubMed) and Google Scholar using search terms connected with Boolean operators. Two separate searches were performed for MetHb and COHb to make the literature research process simpler. For case one (MetHb and COVID-19) the keywords “methemoglobinemia”, “methemoglobinemia”, ”methemoglobin”, “methaemoglobin”, “COVID-19” and “COVID19” were used; for case two (COHb and COVID-19) they were “carboxy-hemoglobinemia”, “carboxyhaemoglobinaemia”, ”carboxyhemoglobin”, “carboxyhaemo-globin”, “COVID-19” and “COVID19”. Relevant studies published in 2020 were searched. In addition, the reference lists of relevant published articles were also manually searched for additional articles.
The result of the literature research was screened for articles (studies or case reports) that report measurement of MetHb or COHb in COVID-19 patients. The exclusion criteria were articles not reporting MetHb or COHb measurements or articles published in non-academic journals, reviews, dissertations or conference abstracts. Articles published on preprint servers were included.