Investigation

Diagnosis of the cause of a lower G.I. bleed on the basis of clinical findings is not sufficiently accurate and hence special investigations are particularly important.

The following protocol may be useful:

• nasogastric tube aspirate: for evidence of a massive upper GI bleed – a lower GI bleed with haemodynamic instability may be indicative of an upper GI bleeding source (1)
• sigmoidoscopy: 10% of lower G.I. bleeds occur within reach of a sigmoidoscope

If sigmoidoscopy is negative:

• colonoscopy:
  • this should be performed as soon as possible
  • emergency preparation of the gut is by administration of 500 ml 10% mannitol, 10 mg metoclopramide and plenty of water; an alternative is picolax
  • observation should be possible in 2-3 hrs

If colonoscopy is negative, consider:

• technetium scintiscan:
  • good at localising a lesion
  • subsequent management would include arteriography and/ or surgery
• mesenteric angiography:
  • a sensitive test if the bleeding is brisk, i.e. > 1-2 ml/min

Reference:

1. Oakland K, Chadwick G, East JE, et al Diagnosis and management of acute lower gastrointestinal bleeding: guidelines from the British Society of GastroenterologyGut 2019;68:776-789.