Colonoscopy is the Test of Choice for This Patient
In a patient presenting with persistent constipation and rectal bleeding for 2-3 months without prior medical history, colonoscopy is the appropriate diagnostic test to exclude colorectal cancer and other significant pathology. 1
Why Colonoscopy is Indicated
The American Gastroenterological Association specifically recommends structural evaluation of the colon in patients with alarm symptoms (blood in stools), abrupt onset of constipation, or those older than 50 years who have not undergone previous colorectal cancer screening. 1 This patient meets criteria for alarm symptoms with persistent rectal bleeding over 2-3 months. 1
A colonoscopy should not be performed in patients without alarm features unless age-appropriate colon cancer screening has not been performed—but this patient HAS alarm features (rectal bleeding), making colonoscopy clearly indicated. 1
Why the Other Options Are Incorrect
Most Likely Diagnosis: Cannot Be Determined Without Investigation
While anal fissure is common in patients with constipation and minor rectal bleeding, symptoms alone cannot reliably predict the source of bleeding. 2 Research shows that among 145 patients aged 40+ with rectal bleeding, few symptoms had statistically significant association with bleeding source, and most bowel symptoms were not helpful in deciding the diagnosis. 2
Colon cancer cannot be excluded based on clinical presentation alone. 3 A prospective study of 297 patients with visible rectal bleeding found that 6.5% had colon cancer and 24% had serious disease (polyps, inflammatory bowel disease, or cancer), with symptoms failing to predict diagnosis. 3
The combination of persistent constipation (2-3 months) with rectal bleeding constitutes an alarm feature requiring full colonic evaluation regardless of presumed benign etiology. 1
CT Scan is Not the Primary Diagnostic Test
CT scan is indicated for acute, severe bleeding with hemodynamic instability or when endoscopy fails to identify a bleeding source. 1, 4 This patient has chronic, minor bleeding—not an acute hemorrhage requiring CT angiography. 4
The American Gastroenterological Association guidelines do not recommend CT as first-line evaluation for chronic constipation with rectal bleeding. 1
Cecal Location Cannot Be Assumed
Without diagnostic evaluation, the location of any potential lesion is purely speculative. 2
While colonic angiodysplasias are most common in the cecum and proximal ascending colon (54%), this applies to a specific pathology (angiodysplasia) and cannot be generalized to all causes of rectal bleeding. 5
Initial Assessment Before Colonoscopy
Before proceeding to colonoscopy, perform:
Digital rectal examination to assess for masses, hemorrhoids, fissures, or blood and evaluate pelvic floor motion during simulated evacuation. 1, 4 However, a normal digital rectal examination does not exclude defecatory disorders or more proximal pathology. 1
Metabolic tests (thyroid-stimulating hormone, glucose, calcium) are not recommended for chronic constipation unless other clinical features warrant them. 1
Critical Pitfall to Avoid
Do not assume benign anorectal pathology (hemorrhoids, fissures) explains the bleeding without full colonic evaluation. 6 A study of 33 patients with intermittent bright red rectal bleeding found that positive findings on rectal examination had no relationship to findings at endoscopy—abnormal findings occurred in 52% of patients with normal rectal exams and 27% with abnormal rectal exams. 6 Colonoscopy resulted in management changes in 48% of patients. 6
Research demonstrates that diagnostic evaluation of rectal bleeding in primary care is often suboptimal, with physicians ordering colonoscopy in only 74% of patients who needed it according to guidelines, and only 56% completing the procedure within a year. 7
Answer to the Multiple Choice Question
The correct answer is (c): The test of choice is colonoscopy. 1