- Blood not obvious, usually because of chronic loss of small amounts of blood. Suspected by iron-deficiency anaemia or by faecal occult blood testing.
- Passage of obvious blood, manifest as haematemesis or haematochezia.
- Describes bleeding that persists or recurs, but where no source can be identified, sometimes despite extensive or repeated investigation.
The existence of obscure GI bleeds is a reflection of the limitations of our investigations. Many previously obscure bleeds would be detected with newer technology such as capsule endoscopy.
Both occult and overt bleeding with an identified sources are dealt with according to the lesion. This leaves obscure-occult (e.g. continued FOB +ve with no identifiable source) and obscure-overt (e.g. frank lower GI bleeding with no identifiable source). The approach to these two types are slightly different.