MUC1 and hypersensitivity pneumonitis: Seven studies reported the association between HP patients and concentrations of KL-6 in an Asian population (19–21, 28–31) The results indicated that KL-6 concentrations were considerably higher in HP patients as compared to the control individuals (SMD = 4.53, 95% CI = 2.66-6.40, I2 = 98%, P<0.0001) (Table 3).