MUC1 and acute respiratory distress syndrome: The median plasma KL-6 level on day 0 (422 u/ml) was significantly increased compared with both normal control individuals (137.1, 95% CI median difference = 31 to 397, P = 0.022) and individuals at risk of ARDS (median = 222 u/ml, 95% CI median difference = 22.4 to 276.4, P = 0.014).