Clinical use
Measurement of faecal alpha-1-antitrypsin may be useful in diagnosing and monitoring protein losing enteropathy in patients in which other causes of protein loss have been excluded and have a normal serum alpha-1-antitrypsin concentration.
Background
Protein losing enteropathy is characterised by the excessive loss of proteins into the gastrointestinal tract (GI) which is excreted in faeces. Most proteins that enter the GI are degraded by proteolytic enzymes, however alpha-1-antitrypsin is a protease inhibitor and is therefore relatively resistant to such enzymes. As such it can pass through the GI tract and remain fairly intact in faeces. Protein losing enteropathy is not a disease state itself, but can arise as a consequence of:
- Increased intestinal pressure due to neoplasia of mesenteric lymph nodes/lymphatics, portal hypertension, congestive heart failure
- Erosive mucosal disease/inflammatory bowel disease such as Crohn’s disease or Ulcerative Colitis
- Non-erosive mucosal or “leaky gut” conditions such as coeliac disease, tropical sprue, Whipple’s disease, connective tissue disorders
Patients present with very low serum protein concentrations (serum albumin loss through the gut is usually around 3% of the total albumin pool, which can rise up to 60% in protein losing enteropathy) with oedema occurring as a consequence of this. Protein losing enteropathy is relatively rare, so it is important that other possible causes of low serum proteins are investigated and excluded. Serum alpha-1-antitrypsin concentration should also be measured, as a low faecal concentration will be expected in patients with reduced serum concentrations, especially those who have alpha-1-antitrypsin deficiency and are S or Z heterozygotes.
Reference ranges
0.00 – 0.48 mg/gww (grams wet weight of faeces)
Patient preparation
None required
Specimen requirements
Stool specimen in a plain container
Limitations/Restrictions
Specimen must be received within 2 hours of collection
Turnaround time
7 days
Analysing laboratory
Protein Reference Unit, South West London Pathology, St George’s Hospital, Blackshaw Road, Tooting, London, SW17 0QT