Page created on September 10, 2021. Last updated on September 14, 2021 at 11:50
Differential diagnosis of bloody stool
Bloody stool includes two different clinical entities: melena (black and/or tarry stool) and haematochezia (passage of bright red blood). Also related is the finding of minimal bright red blood per rectum, where there are small amounts of fresh blood on the toilet paper after wiping.
Haematochezia is typically a sign of lower GI tract bleeding, while melena is typically a sign of upper GI tract bleeding.
- Peptic ulcer
- Oesophageal varices
- Diverticulosis (most common cause overall)
- Inflammatory bowel disease
- Infectious colitis (inflammatory diarrhoea)
- Colorectal cancer
Minimal bright red blood per rectum:
- Anal fissure
- Rectal ulcer
Colonoscopy is the investigation of choice for haematochezia, unless the bleeding is massive and/or the patient is hypovolaemic. In that case, upper endoscopy should be prioritised, as an upper GI bleeding source is more likely. Both colonoscopy and upper endoscopy allow for both diagnosis and, in some cases, treatment of the bleeding.
Digital rectal examination
Digital rectal examination (DRE) is an important investigation in the evaluation of the prostate, rectal bleeding, constipation, and faecal incontinence. It is generally performed in all cases where the patient presents with a gastrointestinal or abdominal complaint. However, the value of using DRE as a routine examination is recently disputed.
Procedure and evaluation
Digital rectal examination must be performed with adequate lubrication and ideally while wearing two gloves on the hand to be used. The patient should lie on their side. The perianal area should be inspected before insertion of the finger; if the patient has a perianal fissure, DRE should not be performed.
Once inside, the whole circumference of the anal canal should be palpated for masses or irregularities. The prostate should be palpated for irregularities, consistency, and tenderness. The patient should be asked to tighten the sphincter, so the examiner can feel for proper tone.
The patient should be examined for Blumer’s sign, the presence of a mass in the Douglas pouch, which may indicate metastasis.
After the examination, the glove should be inspected for faeces or blood. If no blood is visible, the residue on the glove should be tested with a faecal occult blood test.
Distal rectal cancers may be palpable, as may be prostatic pathologies like malignancy, BPH, and prostatitis.