α₁-Antitrypsin, Fecal, Quantitative

Intestinal protein loss is a serious consequence of various systemic or local gastrointestinal diseases (eg, allergies, chronic inflammation; malignancies). These pathologies damage the mucosal integrity and/or cause lymphostasis, thereby leading to an increased transfer of plasma proteins into the bowel lumen. Subsequently, hypoproteinemia accompanied with edema may develop. This condition is diagnosed by exclusion of other sources of protein loss and by proof of an elevated α₁-antitrypsin concentration in stool.

In serum, α₁-antitrypsin represents the majority of serine protease inhibitors and protects tissues from protease damages during inflammation. The protein is synthesized primarily in the liver, but also to a small extent in intestinal macrophages, monocytes, and intestinal epithelial cells. Since α₁-antitrypsin is relatively resistant against enzymatic digestion, the secreted amount in stool reflects the internal concentration of the protein. An elevated α₁-antitrypsin stool concentration is, therefore, a widely recognized marker for intestinal protein loss and for an increased mucosal permeability.