C4A and interstitial lung disease: The likelihood of ILD incidence increased 10.51 times in patients with abnormal levels compared with patients with normal KL-6 levels (OR 10.51, 95%CI 3.7~29.84, P <0.001; Table 4).To further analyse the stability of the adjusted model, we stratified patients by gender, age, smoking status, cough, dyspnoea, and complement C4.