SDC4 and systemic inflammatory response syndrome: The factors related to survival in AE of IPF reported thus far (SIRS score, LDH, KL-6, procalcitonin, severity of hypoxemia and degree of respiratory impairment prior to AE) [48–52] did not reveal associations with death; only baseline serum syndecan-4 level was a prognostic factor, which has interesting ramifications in terms of the pathogenesis of this disease.