MUC1 and COVID-19: A previous meta-analysis evaluating KL-6 in COVID-19 positive and negative subjects also indicated significantly higher KL-6 levels in positive than in healthy subjects (standardized mean difference (SMD) = 1.34; 95%CI: 0.60 to 2.08) with high heterogeneity of data (p < 0.001, I2 = 93%) [22].