Lower gastrointestinal bleeding (LGIB) is defined as that occurring distal to the ligament of Treitz (i.e. from the jejunum, ileum, colon, rectum or anus) and presenting as either hematochezia (bright red blood/clots or burgundy stools) or melena.
The incidence of lower gastrointestinal bleeding is only one-fifth that of the upper gastrointestinal tract and is estimated to be ~24 per 100,000 adults per year. Male and older patients tend to suffer from more severe LGIB 3.
Acute bleeding is defined as bleeding of <3 days' duration, resulting in instability of vital signs, anemia, and/or the need for blood transfusion 3.
Chronic bleeding is defined as slow blood loss over a period of several days or longer, presenting with symptoms of occult fecal blood, intermittent melena or scant hematochezia 3.
Lower gastrointestinal bleeding is usually chronic and the bleeding usually ceases spontaneously (80%) 3.
Although lower GI bleeding can occur at any age, specific disease processes are distinctive for different age groups and familiarity with this can help tailor the diagnostic workup 2,6:
- adolescents and young adults
- older adults
See article: lower gastrointestinal bleeding (differential diagnosis).
Risk factors include 1:
- medications (e.g. NSAID, warfarin)
- recent colonoscopy with polypectomy (post-polypectomy bleeding)
- prior abdominal/pelvic radiation (radiation proctitis/colitis)
- prior surgery
- history of alcoholism or chronic liver disease
- history of abdominal aortic aneurysm with or without surgical repair (causing an aortoenteric fistula)
Most small-bowel hemorrhage occurs in the jejunum (69%), but may also be diffuse or multifocal/multisegmental 8.
Colonoscopy is the first-line investigation for both diagnostic and therapeutic management. CT angiography (CTA), nuclear medicine studies, and angiography can all be used to assess LGIB but have limited sensitivity when bleeding is intermittent or slow. Below are the estimated detectable rates of bleeding by modality 5,6:
- nuclear medicine: ≤0.1 mL/min
- CT angiography: ≥0.35 mL/min
- angiography: ≥0.5 mL/min
CTA and 99mTc-labeled RBC scintigraphy have equal rates of detection of LGIB (at ~40% in one series), but CTA appears to have higher localization rates 7.
On non-contrast CT, hemorrhage may be visualized as circumferential thickening of the bowel wall 8.
CTA provides a relatively non-invasive and effective way of localizing the source of bleeding, especially in patients with continuous bleeding 5.
Studies that have evaluated the use of CTA in the localization of gastrointestinal hemorrhage report a sensitivity of ~90% when there is active bleeding, with detection rates steeply falling to ~45% when the bleeding is intermittent 1.
Again, contraindications apply to patients with renal failure who are at risk of developing contrast-induced nephropathy 1.
Erythrocytes are labeled with technetium-99m, then serial scintigraphy is performed (a.k.a. 99mTc-labeled RBC scintigraphy or tagged red blood cell scan) to detect focal collections of radiolabelled material. It can be performed relatively quickly and may help localize the general area of active bleeding to guide subsequent endoscopy, angiography or surgery 1.
A false-positive result can be produced by a rapid transit of luminal blood so that labeled blood is detected in the colon even though it originated from a more proximal site in the gastrointestinal tract 1.
In patients with lower gastrointestinal bleeding who are haemodynamically-stable and do not have ongoing fresh rectal bleeding, an RBC-labeled Tc99m scan is recommended as a first line of investigation. Catheter angiography is recommended in patients with time-to-positive (TTP) of 9 minutes or less. If TTP is over 9 minutes, the likelihood of detecting the site of bleeding on an angiogram will be markedly low.
Angiography can provide the opportunity for therapeutic intervention at the time of diagnosis 1,2. However, the bleeding rate must be ≥0.5 mL/min to detect extravasation into the gut, which is significantly higher than in nuclear medicine. Additionally, certain patient factors (e.g. contrast allergy, acute/chronic kidney disease) are potential contraindications to angiography 1.
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