Anaema: guaiac occult blood test and faecal alpha 1-antitrypsin were not very helpful in diagnosing GI bleeding.

Clinical bottom line (level 4)

  1. In patients with iron deficiency anaemia, history of suspected melaena or aged over 39 with changed bowel habits, a positive faecal occult blood test made gastrointestinal bleeding slightly more likely (LR + 2.56) , and a negative one made it slightly less likely (LR - 0.39) .
  2. A positive faecal alpha 1-antitrypsin test made a GI bleed slightly more likely (LR + 4.52), and a negative one made it slightly less likely (LR - 0.26) .
Moran et al: Gut 1995; 36: 87-89
Expires June 2003

The study

Setting: general hospital, UK

179 patients (aged ?, ?% male) iron deficiency anaemia, a history suggestive of melaena, or aged >39 years with changed bowel habit

Excluded if
  • known causes of gastrointestinal bleeding
  • protein losing enteropathy
  • overt GI bleeding
Independent blinded reference standard, applied in ?all patients from a consecutive ?appropriate spectrum.
Reference standard:
  • patients with anaemia were investigated by colonoscopy, gastroscopy and distal duodenal biopsy; patients >39 years with changed bowel habits had colonoscopy or rigid sigmoidoscopy and barium enema; patients with history of suspected melaena had colonoscopy and gastroscopy
Diagnostic test: three faecal samples were provided and analysed with guaiac faecal occult blood test and faecal a 1-antitrypsin (measured by radial immunodiffusion). Faecal a 1-antitrypsin concentration >0.58 mg/g wet faecal weight was considered positive

The evidence


diagnostic test gastrointestinal bleed no bleed LR+
(95% CI)		 post-test probability LR-
(95% CI)		 post-test probability
faecal occult blood test 23 39 2.56
(1.82 to 3.61) 		37% 0.39
(0.22 to 0.69) 		8%
faecal a 1-antitrypsin test 25 24 4.52
(3.01 to 6.80) 		51% 0.26
(0.14 to 0.51) 		6%
total 32 139

Comments

  1. Since the authors included patients with a wide variety of presenting complaints, it is possible that the high sensitivity of these tests in one group was masked by the low sensitivity in another group.
  2. A pre-test probability is not appropriate as it is unclear whether the spectrum of patients is appropriate.

Citation

  1. Moran A, Husband D, Jones AF, et al: Diagnostic value of a guaiac occult blood test and faecal alpha 1-antitrypsin. Gut 1995; 36: 87-89
Contributor: Clare Wotton and Musab Hayatli, June 2000
Reviewer: Martin Dawes and Niteesh K Choudhry

Clinical Question.
Patient anaemia, melaena or >39 years with changed bowel habit
Intervention or Exposure guaiac occult blood test and faecal alpha 1-antitrypsin
Comparison colonoscopy etc
Outcome diagnosis of GI bleeding