Knowledge of MetHb and COHb levels in the blood of COVID-19 patients is also relevant to prevent misinterpretations of arterial oxygen saturation values measured with fingertip pulse oximetry (SpO2). This is because MetHb and COHb interfere with the measurement of SpO2. An overestimation of the true arterial oxygenation (SaO2) can occur. In case of a decrease in SaO2 and an increase in MetHb or COHb, SpO2 will diverge more from SaO2 the higher the MetHb and COHb concentration (see Figure 4). For example, assuming a MetHb concentration of around 25% (corresponding to the upper end of the confidence interval of MetHb values in COVID-19 patients reported by Alamdari et al. [21]) and an assumed decrease of SaO2 to 75%, the SpO2 measurements would indicate a falsely too high SpO2 of about 88%. Measurement with pulse CO-oximetry instead of pulse oximetry would circumvent this problem since pulse CO-oximetry is able to non-invasively measure MetHb, COHb, tHb, and the correct SpO2. [83,84,85].