Diagnosing protein-losing enteropathies
|Test Id||Reporting Name||Available Separately||Always Performed|
|A1ATF||Alpha-1-Antitrypsin, 24 Hr, F||No||Yes|
Alpha 1 Antitrypsin
Alpha 1 Antitrypsin (A1A) Clearance, Feces and Serum
Antitrypsin Fecal Clearance
Intestinal Clearance of Alpha-1-Antitrypsin
The recommended procedure for protein-losing enteropathy is A1AFS / Alpha-1-Antitrypsin Clearance, Feces and Serum.
Feces and serum should be shipped together. Specimens shipped separately may delay testing.
Both feces and serum are required.
Blood must be drawn during the stool collection period.
Specimen Type: Serum
Collection Container/Tube: Red top or serum gel
Submission Container/Tube: Plastic vial
Specimen Volume: 1 mL
1. Centrifuge within 2 hours.
2. Aliquot and ship in plastic vial.
Specimen Type: Feces
Supplies: Stool Containers - 24, 48, 72 Hour Kit (T291)
Container/Tube: Stool container
Specimen Volume: Entire collection
1. Collect a 24-hour fecal collection.
2. If no specimen is obtained within 24 hours, extend collection time to 48 to 72 hours. Document time frame.
If not ordering electronically, complete, print, and send a Gastroenterology and Hepatology Client Test Request (T728) with the specimen.
Homogenized feces: 1 mL
Serum: 0.5 mL
|Feces collected in any preservative or fixative||Reject|
|Specimen Type||Temperature||Time||Special Container|
|Fecal||Frozen (preferred)||14 days|
|Serum||Frozen (preferred)||28 days|
Diagnosing protein-losing enteropathies
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.
< or =27 mL/24 hours
FECAL ALPHA-1-ANTRYPSIN CONCENTRATION:
< or =54 mg/dL
SERUM ALPHA-1-ANTRYPSIN CONCENTRATION:
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.
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.
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.
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
Immunonephelometry quantitates the alpha-1-antitrypsin (AAT) contained in a 24-hour fecal collection. From the concentration of feces and serum AAT, a 24-hour clearance is calculated. In the absence of a serum specimen or a timed fecal collection, an AAT fecal concentration will be reported.(Package insert: N Antiserum to Human alpha-1-antitrypsin. Siemens Healthcare Diagnostics Inc; 01/2018)
Monday through Friday
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.
82103 x 2
|Test Id||Test Order Name||Order LOINC Value|
|Result Id||Test Result Name||
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|AAT24||Alpha-1-Antitrypsin, 24 Hr, F||9407-8|