SFTPD and respiratory system disorder: In this investigation, PCT, 8-iso-PGF2α and SP-D in children with severe pneumonia were higher than those in children with non-pneumonic respiratory diseases, which indicated that the combined detection of PCT, 8-iso-PGF2α and SP-D could preliminarily differentiate pneumonia from other non-pneumonic respiratory diseases in children after excluding the interference of other possible infectious diseases.