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”.