Alpha-1-Antitrypsin, Feces, 24 Hour [30523X]

This test measures alpha-1-antitrypsin (AAT) concentration in a 24-hour stool specimen. The result of this test, preferably interpreted jointly with the result of a simultaneous plasma AAT level, may aid in the diagnosis of protein-losing enteropathy [1].

Protein-losing enteropathy is a disorder caused by inflammation or destruction of intestinal mucosa and subsequent increased loss of plasma protein through the gastrointestinal tract. Conditions associated with protein-losing enteropathy include but are not limited to inflammatory bowel disease, lymphoma, Whipple disease, systemic lupus erythematosus, and food allergies [2]. Measurement of radioactive albumin is the "gold standard" for gastrointestinal protein loss but is rarely performed because of the high cost and complex methodology [3]. AAT has a molecular weight similar to that of albumin and is resistant to proteolysis. Therefore, the excretion of AAT in stool can be used to estimate protein loss in the gastrointestinal tract [1,2].

Low stool AAT levels may also be caused by AAT deficiency or impaired hepatic synthesis of AAT; thus, they must be interpreted in conjunction with plasma AAT levels [2]. Abnormal results in patients with intestinal blood loss need to be interpreted carefully owing to the possibly increased AAT clearance [3]. AAT clearance, calculated from AAT concentrations in a 24-hour fecal specimen and a serum specimen, is more reliable for estimating protein loss [4].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. Florent C, et al. Gastroenterology. 1981;81(4):777-780.
2. Sherwood RA, et al. Gastric, intestinal, and pancreatic function. In: Rifai R, et al, eds. Tietz Textbook of Laboratory Medicine. 7th ed. Elsevier Inc; 2022.
3. Strygler B, et al. Gastroenterology. 1990;99(5):1380-1387.
4. Levitt DG, et al. Clin Exp Gastroenterol. 2017;10:147-168.