Recently, Deng et al., declared that serum KL-6 levels in COVID-19 patients were higher than those in healthy patients; serum KL-6 levels in severe/critical COVID-19 patients were especially higher than those in mild patients (median 898.0 vs. 452.1 U/ml, P < 0.001) [17]. The gene discussed is MUC1; the disease is COVID-19.