4.2. Is COHb Increased in COVID-19 Patients?
A significantly higher COHb value in COVID-19 patients compared to reference value of healthy non-smokers (0.5–1.5% for healthy non-smokers [16]) was found in two of the three available reports on COHb and COVID-19 published so far. In the case report of Faisal et al. [20], COHb was 3.2% during the disease course. According to the study of Paccaud et al. [24], COHb rose above the reference range on about the 10th day after hospitalization. Interestingly, this study also clearly demonstrated that at admission, COHb was in the normal range for the COVID-19 patients, while COHb was statistically significantly more elevated on the 31st day of the hospital stay in COVID-19 patients compared to patients suffering from other illnesses. These results are in line with the results of Pawloski et al. [25], who reported that their COVID-19 cohort did not show COHb values above the reference range during the time-span investigated (admission until day seven to nine of the stay). Since Paccaud et al. found that it needs about 10 days until COHb is above the reference range, the too short time-span used by Pawloski et al. to compare COHb values from COVID-19 patients and controls might explain the apparent discrepancy.
In conclusion, COHb can be elevated in COVID-19 patients, especially from about two weeks after onset of the disease. The magnitude of COHb elevation seems to be correlated with the survival probability of the COVID-19 patients.