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HelpTest Code LAB1688 Alpha-1-Antitrypsin Clearance, Feces and Serum
Additional Codes
| Test Name in EPIC | EPIC Test Code | Mnemonic | Mayo Test ID |
|---|---|---|---|
| Alpha-1-Antitrypsin Clearance, Feces and Serum | LAB1688 | A1AFS | A1AFS |
Ordering Guidance
The recommended procedure for protein-losing enteropathy is A1AFS / Alpha-1-Antitrypsin Clearance, Feces and Serum.
Shipping Instructions
Feces and serum should be shipped together. Specimens shipped separately may delay testing.
Specimen Required
Both feces and serum are required. Blood must be drawn during the stool collection period.
Specimen Type: Serum
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube: Red top or serum gel
Submission Container/Tube: Plastic vial
Specimen Volume: 1 mL
Collection Instructions: Within 2 hours of collection, centrifuge and aliquot serum into a plastic vial
Specimen Type: Feces
Supplies: Stool Containers - 24, 48, 72 Hour Kit (T291)
Container/Tube: Stool container
Specimen Volume: Entire collection
Collection Instructions:
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 duration.
Useful For
Diagnosing protein-losing enteropathies
Profile Information
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| AATS | Alpha-1-Antitrypsin, S | No | Yes |
| A1ATF | Alpha-1-Antitrypsin, 24 Hr, F | No | Yes |
Method Name
Nephelometry
Reporting Name
Alpha-1-Antitrypsin ClearanceSpecimen Type
FecalSerum
Specimen Minimum Volume
Homogenized feces: 1 mL; Serum: 0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Fecal | Frozen (preferred) | 14 days |
| Ambient | 14 days | |
| Refrigerated | 14 days | |
| Serum | Frozen (preferred) | 28 days |
| Ambient | 28 days | |
| Refrigerated | 28 days |
Reject Due To
| Gross hemolysis | OK |
| Gross lipemia | Reject |
| Gross icterus | OK |
| Feces collected in any preservative or fixative | Reject |
Clinical Information
Alpha-1-antitrypsin (AAT) is a 54-kDa 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
CLEARANCE:
≤27 mL/24 h
FECAL ALPHA-1-ANTRYPSIN CONCENTRATION:
≤54 mg/dL
SERUM ALPHA-1-ANTRYPSIN CONCENTRATION:
100-190 mg/dL
Interpretation
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
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 less than3 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.
Urine contamination from patients with kidney failure and increased total protein may adversely affect fecal AAT concentration. Suggest catheterizing patient prior to collection if clinically indicated.
Quantitation of specific proteins by nephelometric means may not be possible in lipemic sera due to the extreme light scattering properties of the specimen. Turbidity and particles in the specimen may result in extraneous light scattering signals, resulting in variable specimen analysis.
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.
Method Description
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.(Instruction manual: Siemens Nephelometer II Operations. Siemens, Inc; Version 2.4, 07/2019)
Day(s) Performed
Monday through Friday
Report Available
1 to 3 daysSpecimen Retention Time
2 weeksPerforming 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 x 2
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| A1AFS | Alpha-1-Antitrypsin Clearance | 93419-0 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| AAT24 | Alpha-1-Antitrypsin, 24 Hr, F | 9407-8 |
| AATS | Alpha-1-Antitrypsin, S | 6771-0 |
| CRCLR | Clearance | 18271-7 |
Forms
If not ordering electronically, complete, print, and send a Gastroenterology and Hepatology Test Request (T728) with the specimen.