Specimen Collection
1 g Collect Faeces (Random)
Reference Intervals
Reference interval:
<0.5 mg/g wet weight (children >1yrs old and Adult).
Children less than 1yr old - reference interval to be determined
Uncertainty of measurement: 40
%
Turnaround Time: Within 4 weeks
Up to 8 weeks if further dilutions are required. Please contact the laboratory if more urgent processing is required.
Assay Method
Alpha-1 antitrypsin (AAT) is extracted from faeces and assayed by an enzyme-linked immunosorbent assay (ELISA) using an
Immundiagnostik kit
Diagnostic Use and Interpretation
Faecal alpha1-antitrypsin (FAAT) can normally be found in low concentrations in stool. It is believed that some of the FAAT comes from liver-derived circulating AAT in a pure form or as AAT-protease complex. It has also been proposed that some FAAT are synthesized locally from gut epithelial cells. The expression of these gut derived variants differ between individuals and under different pathological states.
AAT is not reabsorbed in the gut and is resistant to luminal proteolysis. These properties render it used as a marker for Protein Losing Enteropathy (PLE). PLE can occur in diseases affecting gastrointestinal mucosa e.g. inflammatory bowel diseases, infective diarrhoea, coeliac disease or secondary to systemic burns. Conditions causing elevated lymphatic pressure e.g. intestinal lymphangietasia, intestinal lymphoma, congestive heart failure, post Fontan cardiac surgery can also cause PLE. Giant hypertrophic gastropathy (Menetrier's disease) or Zollinger-Ellison syndrome although can cause gastric protein loss but because of low gastric pH, AAT are degraded thus FAAT is not useful for these conditions. FAAT has also been used for monitoring e.g. heparin therapy in PLE.
Diarrhoea per se e.g. caused by lactulose laxative can already induce increase in FAAT. Furthermore, excessive liquid from watery diarrhoea can reduce sensitivity to pick up abnormal gut protein loss as our current FAAT method report in mg/gram wet stool. It is desirable to have non-diarrhoeal stool samples for proper FAAT testing.
Neonates less than 1 wk old have high FAAT from meconium contamination. Breast or formula fed infants have slightly higher FAAT compare with older children and adults.
It is difficult to interpret FAAT from patients with significant genetic alpha1-antitrypsin deficiency.
Concomitant evaluation for faecal occult blood may improve clinical interpretation of FAAT results - gastrointestinal bleeding can lead to false elevation of FAAT simply because of leakage of circulating AAT into bowels. On the other hand, simultaneous mucosal protein loss and blood loss from the same gut pathology is also possible so possibility of PLE in the presence of positive faecal occult blood and raised FAAT should not be totally disregarded.
References:
- Greenwald DA. Protein losing enteropathy in Sleisenger and Fordtran's Gastrointestinal and Liver disease : Pathophysiology/Diagnosis/Treatment. 8th edition. P.557-563. Feldman M, Friedman LS, Brandt LJ (eds) Saunders Elsevier Inc.
- Faust D. Determination of alpha 1-proteinase inhibitor by a new enzyme-linked immunosorbent assay in feces, serum and an enterocyte-like cell line. Zeitschrift fur gastroenterology 2001 Sept 39(9): 769-74
- Choudhary S et al. Measurement of faecal alpha 1-antitrypsin : Methodologies and clinical application. J Gastro Hepat 1996; 11:311-318
- Strygler B et al alpha 1-antitrypsin excretion in stool in normal subjects and in patients with gastrointestinal disorders. Gastroenterol 1990; 99:1380-87
Contact Information
Emails to
chemicalpathologist@adhb.govt.nz
will receive priority attention from the on-call chemical pathologist.
If the query concerns a specific patient please include the NHI number in your email.
If email is not a suitable option, please contact the on-call chemical pathologist via
Lablink (Auckland City Hospital ext. 22000 or 09-3078995).
Individual chemical pathologists may be contacted but will not be available at all times.
After-hours
: contact
Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.
Dr Cam Kyle (Clinical Head):
CampbellK@adhb.govt.nz
ext 22052
Dr Weldon Chiu:
WeldonC@adhb.govt.nz
ext. 23427
Dr Leah Ha:
LHa@adhb.govt.nz
ext. 23427
Dr Samarina Musaad:
SamarinaM@adhb.govt.nz
ext. 22402
Dr Leo Lam:
ChiSingL@adhb.govt.nz
ext 22574
Specimen Transport Instructions for Referring Laboratories
Random stool sample required.
Specimens should be transported frozen and are stable for up to four weeks at -20oC