Alpha-1-antitrypsin - faeces

Random: 5 g faeces; a test for occult blood in faeces should also be performed to exclude bleeding as a cause of an elevated α1-antitrypsin.

A clearance study requires a three day faecal collection (faeces should be frozen during collection period if possible) plus 5 mL blood in a plain tube for serum α1-antitrypsin assay.

Random: <1.5 mg/g dry weight
Clearance: <12.5 mL/day.

If α1-antitrypsin is elevated in the absence of a positive occult blood test, increased loss of plasma proteins from the bowel is present. If occult blood is positive, the α1-antitrypsin is at least partly derived from blood loss, but a coexistent protein-losing enteropathy cannot be excluded.
An approximate assessment of intestinal plasma protein loss can be made by estimating the clearance of α1-antitrypsin from plasma into faeces (that is, the volume of plasma cleared of α1-antitrypsin per day).