and 111.7 mm Hg. The sensitivity was 76.5% and 85.3%， and the specificity was 79.6% and 98.6%. The combined sensitivity and specificity of serum IL-6 level and P(A-a)O2 for predicting the risk of ARDS were 77.5% and 98.1%. The AUC was 0.996， which did not significantly differ from that of P(A-a)O2 (P > 0.05). Conclusions Upon admission， detection of serum IL-6 level and P(A-a)O2 can predict the incidence of ARDS in patients with influenza A H1N1 pneumonia. P(A-a)O2 performs better than serum IL-6 level. The combination of serum IL-6 level and P(A-a)O2 does not differ from P(A-a)O2 alone. However ......