CA1A - Clinical: Alpha-1-Antitrypsin Clearance, Feces and Serum

Test Catalog

Test Name

Test ID: CA1A    
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 (A1A) 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. A1A clearance is reliable for measuring protein loss distal to the pylorus.


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.

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.

Clearance: < or =27 mL/24 hours

Fecal alpha-1-antitrypsin concentration: < or =54 mg/dL

Serum alpha-1-antitrypsin concentration: 100-190 mg/dL

Interpretation Provides information to assist in interpretation of the test results

Elevated alpha-1-antitrypsin (A1A) 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 A1A clearance values greater than 50 mL/24 hours and A1A stool concentrations above 100 mg/mL.


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 stool collection or a contemporary serum specimen, the fecal concentration of alpha-1-antitrypsin (A1A) can be used as a surrogate marker. The clearance is preferred in order to normalize the large range of serum A1A concentrations and the variability in random stool A1A concentration.

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, et al: Intestinal Clearance of alpha 1-antitrypsin. A sensitive method for the detection of protein losing enteropathy. Gastroenterology 1981;81:777-780

2. Crossley JR, Elliott RB: Simple method for diagnosing protein-losing enteropathy. Br Med J 1977;1:428-429

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