Samples at the time of suspected NEC had a median (IQR) IAP activity of 355 (172-608) μmol/min/g (95% CI, 172-608 μmol/min/g) of stool protein, and IAP activity in PCA-matched control samples had a median (IQR) of 613 (210-1465) μmol/min/g (95% CI, 386-723 μmol/min/g) of stool protein. Here, ALPI is linked to necrotizing enterocolitis.