Test Catalog

Test ID: A1AFS    
Alpha-1-Antitrypsin Clearance, Feces and Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosing protein-losing enteropathies

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Alpha-1-antitrypsin (AAT) is a 54kDa glycoprotein that is resistant to degradation by digestive enzymes and is, therefore, used as an endogenous marker for the presence of blood proteins in the intestinal tract. AAT clearance is reliable for measuring protein loss distal to the pylorus. A serum sample is required to interpret results as a serum deficiency of AAT would make the AAT fecal excretion lower and could invalidate the test utility.


Gastrointestinal protein enteropathy has been associated with regional enteritis, sprue, Whipple intestinal lipodystrophy, gastric carcinoma, allergic gastroenteropathy, intestinal lymphangiectasia, constrictive pericarditis, congenital hypogammaglobulinemia, and iron deficiency anemia associated with intolerance to cow's milk. Increased fecal excretion of AAT can be found in small and large intestine disease and is applicable to adult and children.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


< or =27 mL/24 hours



< or =54 mg/dL



100-190 mg/dL

Interpretation Provides information to assist in interpretation of the test results

Elevated alpha-1-antitrypsin (AAT) clearance suggests excessive gastrointestinal protein loss. The positive predictive value of the test has been found to be 97.7% and the negative predictive value is 75%.


Patients with protein-losing enteropathies generally have AAT clearance values greater than 50 mL/24 hours and AAT fecal concentrations above 100 mg/dL.


Borderline elevations above the normal range are equivocal for protein-losing enteropathies.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

In the absence of either a 24-hour fecal collection or a contemporary serum specimen, the fecal concentration of alpha-1-antitrypsin (AAT) can be used as a surrogate marker. The clearance test is preferred as it normalizes the large range of serum AAT concentrations and the variability in random fecal AAT concentrations.


When gastric loss of AAT is suspected (eg, Menetrier disease), AAT clearance is not a reliable indicator of protein loss as AAT is sensitive to pH <3 and rapidly destroyed. When gastric protein loss is suspected and the AAT clearance is normal, the recommendation is to repeat testing after starting an acid suppressive medication regime.

Supportive Data

Protein-losing enteropathy has been studied by intravenous injection of radioactive chromium chloride or labeled human serum albumin. The correlation between radiochromium and stool alpha-1-antitrypsin clearance has been measured with excellent correlation coefficients.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Florent C, L'Hirondel C, Desmazures C, Aymes C, Bernier JJ: Intestinal clearance of alpha 1-antitrypsin. A sensitive method for the detection of protein losing enteropathy. Gastroenterology. 1981 Oct;81(4):777-780

2. Crossley JR, Elliott RB: Simple method for diagnosing protein-losing enteropathies. Br Med J. 1977 Feb 12;1(6058):428-429

3. Perrault J, Markowitz H: Protein-losing gastroenteropathy and the intestinal clearance of serum alpha-1-antitrypsin. Mayo Clin Proc. 1984 Apr;59(4):278-279

4. Schmidt PN, Blirup-Jensen S, Svendsen PJ, Wandall JH: Characterization and quantification of plasma proteins excreted in faeces from healthy humans. Scand J Clin Lab Invest. 1995 Feb;55(1):35-45

5. Davidson NO: Intestinal lipid absorption. In: Yamada T, Alpers DH, Kaplowitz N, eds. Textbook of Gastroenterology. JB Lippincott; 2003:413

6. Rybolt AH, Bennett RG, Laughon BE, Thomas DR, Greenough WB III, Bartlett JG: Protein-losing enteropathy associated with Clostridium difficile infection. Lancet. 1989 Jun 17;1(8651):1353-1355

7. Molina JF, Brown RF, Gedalia A, Espinoza LR: Protein losing enteropathy as the initial manifestation of childhood systemic lupus erythematosus. J Rheumatol. 1996 Jul;23(7):1269-1271

8. Umar SB, DiBaise JK: Protein-losing enteropathy: case illustrations and clinical review. Am J Gastroenterol. 2010 Jan;105(1):43-49

9. Levitt DG, Levitt MD: Protein losing enteropathy: comprehensive review of the mechanistic association with clinical and subclinical disease states. Clin Exp Gastroenterol. 2017 Jul;10:147-168

10. Murray FR, Morell B, Biedermann L, Schreiner P: Protein-losing enteropathy as precursor of inflammatory bowel disease: A review of the literature. BMJ Case Rep. 2021 Jan 11;14(1):e238802