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 protocols may be useful: (1,2)

• 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
• 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 Gastroenterology. Gut. 2019 May;68(5):776-89.
2. Sengupta N, Feuerstein JD, Jairath V, et al. Management of patients with acute lower gastrointestinal bleeding: an updated ACG guideline. Am J Gastroenterol. 2023 Feb 1;118(2):208-31.