What labs and imaging are indicated for a patient presenting with rectal bleeding characterized by dark chocolate-colored stools and a positive fecal occult blood test (FOBT)?

From the Guidelines

For rectal bleeding with dark chocolate appearance and positive fecal occult blood test, I recommend ordering a complete blood count (CBC) to assess for anemia, basic metabolic panel (BMP) to evaluate kidney function, coagulation studies (PT/INR, PTT) to rule out bleeding disorders, and type and screen in case blood transfusion is needed, as suggested by the guidelines for anorectal emergencies 1. Imaging should include an abdominal and pelvic CT scan with contrast to evaluate for masses, inflammation, or vascular abnormalities.

• The dark chocolate appearance of the blood suggests it originated from the upper GI tract or right colon, as blood becomes darker when exposed to digestive enzymes over time.
• The positive fecal occult blood test confirms the presence of blood but doesn't indicate the source, as stated in the guidelines for screening and surveillance for the early detection of colorectal cancer and adenomatous polyps 1. Colonoscopy is the gold standard diagnostic test and should be arranged promptly, as it allows direct visualization and potential intervention, according to the guidelines for anorectal emergencies 1. Upper endoscopy (EGD) may also be warranted if an upper GI source is suspected, as suggested by the guidelines for anorectal emergencies 1. These tests will help identify potentially serious conditions such as colorectal cancer, inflammatory bowel disease, diverticular bleeding, or angiodysplasia that require prompt diagnosis and treatment.
• The estimated risk of CRC in patients with rectal bleeding has been reported to range from 2.4 to 11%, hence a full colonoscopy may be necessary to identify such a source, as stated in the guidelines for anorectal emergencies 1.
• A randomized trial from Laine et al. showed that up to 15% of patients presenting with serious hematochezia have an upper gastrointestinal source of bleeding identified at upper endoscopy, highlighting the importance of considering an upper GI source in patients with rectal bleeding 1.

From the Research

Labs and Imaging for Rectal Bleeding

For a patient presenting with rectal bleeding characterized by dark chocolate-colored stools and a positive fecal occult blood test (FOBT), the following labs and imaging are indicated:

• Complete blood count (CBC) to evaluate for anemia
• Electrolyte panel to assess for any electrolyte imbalances
• Liver function tests (LFTs) to evaluate for any liver dysfunction
• Coagulation studies to assess for any coagulopathy
• Stool studies to evaluate for any infectious causes of bleeding

Imaging Studies

The following imaging studies may be indicated:

• Colonoscopy: This is the gold standard for evaluating the colon and rectum for any lesions or bleeding sources 2, 3
• Esophagogastroduodenoscopy (EGD): This may be indicated if the patient has a history of upper gastrointestinal bleeding or if the colonoscopy is negative 2
• Computed tomographic (CT) colonography: This may be indicated if the patient is unable to undergo colonoscopy or if the colonoscopy is incomplete 4
• Capsule endoscopy: This may be indicated if the patient has a history of small bowel bleeding or if the colonoscopy and EGD are negative 2

Diagnostic Yield of Colonoscopy

The diagnostic yield of colonoscopy for cancers and adenomas by indication is as follows:

• Bleeding indications (positive fecal occult blood test, emergent or nonemergent rectal bleeding, melena with a negative upper endoscopy and iron deficiency anemia): 1 per 9 to 13 colonoscopies 3
• Nonbleeding colonic symptoms: 1 per 109 colonoscopies 3
• Screening colonoscopy: 1 per 64 colonoscopies for males more than 60 years old 3

Fecal Occult Blood Test (FOBT)

The FOBT is a useful screening tool for colorectal cancer, with a sensitivity of 13% to 81% and a specificity of 90% to 95% 5, 4. However, the test has a high false positive rate, and a positive result should be followed by a colonoscopy to confirm the diagnosis 6, 4.