The permeability of tubular epithelial cells is related with the severity of renal injury, When the kidney suffers injury, and the more severely the renal epithelial cell barrier is damaged, the more SP-D protein would leak into blood from tubular lumen,which may explain the significant correlation between higher serum SP-D levels and higher stage of renal injury in AKI patients. This evidence concerns the gene SFTPD and acute kidney injury.