Alpha 1-antitrypsin, a reliable endogenous marker for intestinal protein loss and its application in patients with Crohn's disease.

Intestinal protein loss is generally determined by radio-labelled macromolecules. Alpha 1-antitrypsin has been proposed as an endogenous marker for protein losing enteropathy, but different opinions exist about its reliability. In 25 patients with Crohn's disease faecal protein loss was studied with intestinal alpha 1-antitrypsin (alpha 1AT) clearance. Simultaneously, in 10 patients alpha 1AT clearance was compared with faecal 51Cr clearance after intravenous 51Cr-albumin injection. There was a linear relation (p less than 0.05) between alpha 1AT clearance and 51Cr clearance in these cases. In all patients alpha 1AT clearance was raised above control values. alpha 1AT clearance, however, did not correlate with the activity index of Crohn's disease. This index does not contain direct criteria of intestinal inflammation, does not take into account localisation or extent of inflammation, and includes complications such as extraintestinal manifestations, fistuli, stenoses not necessarily related to actual mucosal involvement. It is concluded that alpha 1AT is a reliable marker for intestinal protein loss and that the intestinal changes of Crohn's disease generally lead to an increased protein exudation into the gut.