Routine blood tests showed that the following characteristics were significantly different between non-severe and severe pneumonia patients: red blood cells; hemoglobin; white blood cells (WBCs); basophil count; basophil percentage; monocyte and neutrophil count; CD4, CD8, CD4/CD8, CD9, and CD16/CD56 count/percentage; immunoglobulin A (IgA); and IgM. Here, CD9 is linked to susceptibility to pneumonia measurement.