Test Summary

This test measures alpha-1-antitrypsin (AAT) concentration in a random stool specimen and may help screen for protein-losing enteropathy [1]. An AAT level measured in a 24-hour stool specimen and interpreted jointly with a simultaneous blood AAT level is generally preferred for the diagnosis of protein-losing enteropathy [2].

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 [3]. Measurement of radioactive albumin is the "gold standard" for gastrointestinal protein loss but is rarely performed because of the high cost and complex methodology [4]. 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 [2,3].

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 [3]. Abnormal results in patients with intestinal blood loss need to be interpreted carefully owing to the possibly increased AAT clearance [4].

An AAT level measured in a random stool specimen may not accurately reflect daily AAT excretion [2]. AAT clearance, calculated from AAT concentrations in a 24-hour fecal specimen and a serum specimen, is more reliable for estimating protein loss [5].

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

References
1. Thomas DW, et al. Gastroenterology. 1981;80(4):776-782.
2. Florent C, et al. Gastroenterology. 1981;81(4):777-780.
3. 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.
4. Strygler B, et al. Gastroenterology. 1990;99(5):1380-1387.
5. Levitt DG, et al. Clin Exp Gastroenterol. 2017;10:147-168.

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