In an 85-year-old male with chronic diarrhea, anemia, and elevated fecal calprotectin despite prior normal colonoscopies, what diagnostic work‑up and management should be pursued?

Proceed with Scheduled Colonoscopy and Comprehensive Anemia Work-up

In this 85-year-old male with chronic diarrhea, anemia, and rising fecal calprotectin (278 μg/g), the scheduled colonoscopy with biopsies is the correct next step, followed by systematic evaluation for the anemia and consideration of small bowel imaging if colonoscopy is unrevealing.

Diagnostic Approach

Elevated Fecal Calprotectin Interpretation

The rising fecal calprotectin from 120 to 278 μg/g indicates active colonic inflammation that requires endoscopic confirmation 1, 2. In elderly patients presenting with chronic diarrhea, colonoscopy with histologic confirmation remains the cornerstone of diagnosis because this population has higher rates of conditions that mimic inflammatory bowel disease (IBD), including colorectal cancer, ischemic colitis, segmental colitis associated with diverticulosis, and microscopic colitis 1.

• Fecal calprotectin >150 μg/g has 71% sensitivity and 69% specificity for detecting moderate-to-severe endoscopic inflammation 3
• At 250 μg/g cutoff, sensitivity is 67% and specificity is 73% 3
• The positive predictive value is low in general populations, but the negative predictive value is high (89.8-97.3%) 4

Critical Colonoscopy Requirements

Obtain biopsies from multiple colonic segments, specifically including the right and left colon (not just rectum) to exclude microscopic colitis 2. This is essential because:

• Microscopic colitis (lymphocytic or collagenous colitis) is highly prevalent in patients ≥60 years with chronic diarrhea 5
• Endoscopic appearance may be completely normal despite active histologic inflammation 5
• Rectal biopsies alone may miss the diagnosis 5

Differential Diagnosis Priorities in Elderly Patients

The diagnostic work-up must systematically exclude 1:

1. Colorectal cancer - higher prevalence in this age group
2. Ischemic colitis - especially given cardiovascular medications (atenolol, valsartan)
3. Segmental colitis associated with diverticulosis - if diverticulosis present on colonoscopy
4. Microscopic colitis - requires histologic diagnosis
5. IBD (Crohn's disease or ulcerative colitis) - can present de novo in elderly
6. Medication-induced colitis - review all medications, though current list shows no obvious culprits

Anemia Evaluation

The anemia requires concurrent systematic investigation 6:

Essential Testing

• Complete iron studies (serum iron, ferritin, TIBC, transferrin saturation)
• Celiac serology (tissue transglutaminase IgA with total IgA) - should be done before or at time of upper endoscopy 6
• Vitamin B12 and folate levels
• Reticulocyte count

Upper Endoscopy Considerations

Since upper endoscopy is already scheduled, ensure:

• Small bowel biopsies from duodenum (even if mucosa appears normal) to evaluate for celiac disease if serology is positive or if duodenal abnormalities are visualized 6
• Gastric biopsies to assess for autoimmune atrophic gastritis (given age and anemia)
• Evaluation for sources of blood loss

If Colonoscopy and Upper Endoscopy Are Unrevealing

Small Bowel Evaluation

Consider small bowel capsule endoscopy (SBCE) if:

• Anemia persists despite iron supplementation
• Fecal calprotectin remains elevated
• No source identified on bidirectional endoscopy

Recent evidence shows SBCE has superior diagnostic yield compared to MR enterography for isolated small bowel Crohn's disease, identifying disease in 79.4% of patients with elevated fecal calprotectin and normal colonoscopy 7. SBCE detected small bowel Crohn's disease in 42 patients where MRE was negative 7.

Alternative Diagnoses to Consider

If endoscopic evaluation is negative:

1. Bile acid diarrhea - consider SeHCAT testing or serum 7α-hydroxy-4-cholesten-3-one 2
2. Medication review - though aspirin is contraindicated due to prior subarachnoid hemorrhage, review all medications including recent additions
3. Infectious causes - though C. difficile and routine pathogens were negative, consider:
   • Giardia (already tested, negative)
   • Chronic parasitic infections if travel history
   • Small intestinal bacterial overgrowth (breath testing)

Management Considerations

Symptomatic Treatment

The prescribed loperamide is appropriate for symptom control while awaiting definitive diagnosis 8.

Iron Supplementation

Initiate oral iron supplementation immediately given documented anemia and no prior treatment 6. The patient has never received iron despite known anemia - this is a significant gap in care.

Monitoring Strategy

• Repeat fecal calprotectin 3-6 months after treatment initiation to assess response 9
• If fecal calprotectin normalizes (<150 μg/g), this reliably indicates resolution of inflammation 9

Common Pitfalls to Avoid

1. Do not rely solely on fecal calprotectin to guide treatment - endoscopic confirmation is essential in elderly patients given the broad differential 1
2. Do not skip colonic biopsies - microscopic colitis requires histologic diagnosis and is easily missed 5, 2
3. Do not forget small bowel evaluation if bidirectional endoscopy is negative - isolated small bowel Crohn's disease is increasingly recognized 7
4. Do not delay iron supplementation - initiate empirically while pursuing diagnostic work-up 6

The scheduled colonoscopy on the upcoming date is appropriately timed and should proceed as planned with comprehensive biopsy sampling.