What is the differential diagnosis for a 22-year-old immigrant patient presenting with bright red blood per rectum, constipation, and sensation of incomplete defecation, with lab results showing anemia (low hemoglobin), microcytosis (decreased Mean Corpuscular Volume (MCV)), hypochromia (decreased Mean Corpuscular Hemoglobin (MCH)), elevated Red Cell Distribution Width (RDW), and increased inflammatory markers (elevated Sedimentation Rate (set rate) and C-Reactive Protein (CRP))?

Differential Diagnosis for a 22-Year-Old Immigrant with Bright Red Blood Per Rectum, Constipation, and Microcytic Anemia

This patient requires urgent colonoscopy to evaluate for inflammatory bowel disease (IBD), particularly given the constellation of rectal bleeding, incomplete evacuation, microcytic anemia with elevated inflammatory markers (ESR 13, CRP 0.67), and immigrant status from an endemic area. 1

Critical Red Flags Present

This patient exhibits multiple alarm features that mandate aggressive investigation rather than conservative management:

• Anemia with microcytosis (Hemoglobin 12.8 g/dL, MCV 59, MCH 19) in a young male indicates chronic blood loss 1
• Elevated inflammatory markers (ESR 13, CRP 0.67) suggest active intestinal inflammation 1
• Elevated RDW (16.7) indicates mixed or evolving anemia patterns 1
• Bright red blood per rectum with incomplete evacuation raises concern for distal colonic pathology 1
• Young immigrant patient increases risk for infectious colitis, particularly tuberculosis, and early-onset IBD 2

Primary Differential Diagnosis

1. Inflammatory Bowel Disease (Most Likely)

Ulcerative colitis or Crohn's disease is the leading diagnosis given the combination of rectal bleeding, constipation (which can occur with distal colitis), incomplete evacuation, microcytic anemia, and elevated inflammatory markers in a young patient. 1, 2

• The microcytic anemia with normal iron studies (ferritin 58.5, iron saturation 31%) is characteristic of anemia of chronic disease superimposed on iron deficiency in IBD 1, 3
• In the context of inflammation (elevated CRP), ferritin up to 100 μg/L can still indicate iron deficiency, making this patient's ferritin of 58.5 consistent with true iron deficiency masked by inflammation 1, 4
• The elevated RDW suggests mixed anemia patterns common in active IBD 1
• Colonoscopy with biopsies is mandatory for diagnosis 1

2. Infectious Colitis (Critical to Exclude)

Tuberculosis must be specifically excluded given the patient's immigrant status, as intestinal TB can perfectly mimic Crohn's disease with similar endoscopic and histologic features. 2

• Stool studies for ova and parasites are essential given geographic origin 1
• Consider testing for Entamoeba histolytica, Giardia, and other endemic parasites 1
• Tuberculosis testing (QuantiFERON-Gold or PPD, chest X-ray) should be performed before initiating any immunosuppressive therapy 2

3. Colorectal Neoplasia

Although less common at age 22, the presence of alarm features (bleeding, anemia, incomplete evacuation) mandates exclusion of malignancy. 1

• Colonoscopy is indicated regardless of age when alarm features are present 1
• Adenomatous polyps occur in 3% of young patients with rectal bleeding 5

4. Anorectal Pathology (Less Likely as Sole Diagnosis)

While hemorrhoids and anal fissures are common causes of bright red rectal bleeding, they do not explain the systemic findings of anemia, elevated inflammatory markers, or incomplete evacuation sensation. 1, 6

• Internal hemorrhoids may coexist with IBD (found in 26.9% of patients) but are unlikely to cause this degree of anemia 5
• The sensation of incomplete defecation is more consistent with rectal inflammation than simple hemorrhoids 1

Essential Diagnostic Workup

Immediate Laboratory Studies

• Stool studies: Ova and parasites (×3), Clostridium difficile toxin, fecal calprotectin, stool culture 1, 2
• Tuberculosis screening: QuantiFERON-Gold or PPD, chest X-ray 2
• Vitamin B12 and folate levels: To evaluate for concurrent deficiencies, particularly if small bowel Crohn's disease is present 1
• Reticulocyte count: To assess bone marrow response to anemia 1

Endoscopic Evaluation

Colonoscopy with multiple biopsies is the definitive diagnostic test and should be performed urgently given the alarm features. 1

• Full colonoscopy is required (not just sigmoidoscopy) to assess extent of disease 1
• Multiple biopsies from affected and unaffected areas are essential 1
• Biopsies should be sent for both routine histology and mycobacterial culture if TB is suspected 2

Critical Pitfalls to Avoid

• Do not attribute symptoms solely to hemorrhoids without excluding inflammatory or neoplastic disease in the presence of anemia and elevated inflammatory markers 1, 7
• Do not assume normal ferritin excludes iron deficiency in the setting of inflammation; ferritin up to 100 μg/L may still indicate iron deficiency when CRP is elevated 1, 4
• Do not delay colonoscopy based on young age when alarm features are present 1
• Do not start empiric IBD treatment before excluding tuberculosis in immigrant patients, as immunosuppression can cause disseminated TB 2
• Do not perform only flexible sigmoidoscopy; full colonoscopy is required to assess for proximal disease 1

Management Pending Diagnosis

• Initiate iron replacement therapy with intravenous iron preferred over oral formulations given the severity of anemia and likely IBD diagnosis 4, 3
• Avoid oral iron until IBD is excluded, as non-absorbed iron can worsen intestinal inflammation 3
• Expedite colonoscopy within 2 weeks given alarm features 1