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HelpMayo Test ID A1AF Alpha-1-Antitrypsin, Random, Feces
Ordering Guidance
The preferred test for diagnosing protein-losing enteropathies is A1AFS / Alpha-1-Antitrypsin Clearance, Feces and Serum.
Specimen Required
Supplies:
-Stool container, Small (Random), 4 oz (T288)
-Stool Collection Kit, Random (T635)
Container/Tube: Stool container
Specimen Volume: 5 g
Collection Instructions: Collect a random fecal specimen.
Useful For
Diagnosing protein-losing enteropathies, especially when used in conjunction with serum alpha-1-antitrypsin (AAT) levels as a part of AAT clearance studies
Method Name
Nephelometry
Reporting Name
Alpha-1-Antitrypsin, Random, FSpecimen Type
FecalSpecimen Minimum Volume
Homogenized Stool: 1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Fecal | Frozen (preferred) | 14 days | |
| Ambient | 14 days | ||
| Refrigerated | 14 days |
Reject Due To
| Feces collected in any preservative or fixative | Reject |
Clinical Information
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 adults and children.
Reference Values
≤54 mg/dL
Interpretation
Patients with protein-losing enteropathies generally have alpha-1-antitrypsin fecal concentrations over 100 mg/dL.
Borderline elevations above the normal range are equivocal for protein-losing enteropathies.
Cautions
The clearance studies using 24-hour fecal specimens and serum determinations are preferred as it normalizes the large range of serum alpha-1-antitrypsin (AAT) concentrations and the variability in random fecal AAT concentrations. In the absence of either a 24-hour fecal collection or a contemporary serum specimen, the fecal concentration of AAT can be used as a surrogate marker.
Clinical Reference
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. 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
5. 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
Method Description
Immunonephelometry quantitates the alpha-1-antitrypsin (AAT) contained in a fecal specimen. In the absence of a timed fecal collection, an AAT fecal concentration will be reported.(Instruction manual: Siemens Nephelometer II Operations. Siemens, Inc; Version 2.3, 2008; Addendum to the Instruction Manual 2.3, 08/2017)
Day(s) Performed
Monday through Friday
Report Available
1 to 3 daysSpecimen Retention Time
14 days; supernatant aliquot only, the feces are discarded after processingPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
82103
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| A1AF | Alpha-1-Antitrypsin, Random, F | 9407-8 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| AAT_F | Alpha-1-Antitrypsin, Random, F | 9407-8 |