Should I repeat iron studies and a complete blood count now in a 77‑year‑old man with new diarrhea, positive Clostridioides difficile infection, occult gastrointestinal bleeding, and previously normal iron studies despite chronic anemia?

Yes, Repeat Iron Studies and CBC Now

In a 77-year-old man with new C. difficile infection, positive occult blood, and chronic anemia, you should absolutely repeat both CBC and complete iron studies now, as the clinical picture has fundamentally changed with new GI bleeding and his iron status may have deteriorated significantly from one year ago. 1

Why Repeat Testing is Essential

Changed Clinical Context Demands Reassessment

• The presence of occult GI bleeding represents new active pathology that warrants full investigation regardless of previous iron studies 1
• British Society of Gastroenterology guidelines emphasize that any evidence of active undiagnosed pathology—including ongoing GI blood loss—requires further investigation even when previous workups were negative 1
• The combination of positive occult blood and diarrhea in an elderly patient significantly increases the likelihood of serious underlying GI pathology requiring identification 2, 3

Iron Deficiency Can Develop Rapidly

• Iron studies from one year ago are outdated in the context of new GI bleeding—the British Society of Gastroenterology suggests that investigations older than 2 years should be repeated, and your patient has new bleeding making even the one-year interval too long 1
• Chronic occult GI bleeding commonly manifests as iron deficiency anemia, and previous normal iron studies do not exclude current iron deficiency 3, 4
• The minimum workup for anemia includes red blood cell indices (RDW, MCV), reticulocyte count, serum ferritin, transferrin saturation, and CRP to distinguish between iron deficiency anemia and anemia of chronic disease 1

Specific Tests to Order Now

Complete Blood Count with Indices

• Hemoglobin to assess current anemia severity 1
• MCV and MCH to detect microcytosis and hypochromia suggesting iron deficiency 1
• RDW (red cell distribution width) which increases in iron deficiency 1
• Reticulocyte count to assess bone marrow response 1

Iron Studies Panel

• Serum ferritin (the single most useful marker of iron deficiency) 1
• Transferrin saturation to confirm iron deficiency, especially if ferritin is equivocal 1
• CRP to assess for inflammation, as C. difficile infection can cause anemia of chronic disease which may mask iron deficiency 1

Critical Next Steps After Lab Results

If Iron Deficiency is Confirmed

• Bidirectional endoscopy (both colonoscopy and upper endoscopy) is strongly recommended by the American Gastroenterological Association for iron deficiency anemia with positive occult blood, as dual pathology occurs in 10-15% of cases 2
• Do not attribute the positive occult blood solely to C. difficile colitis without complete evaluation—physicians should not attribute positive fecal occult blood to any condition without further evaluation 3
• Small bowel biopsies during upper endoscopy should be obtained to rule out celiac disease, present in 2-3% of iron deficiency anemia cases 2

Common Pitfall to Avoid

• Do not accept C. difficile infection as the sole explanation for occult blood without completing full GI evaluation, especially in a 77-year-old man where colorectal cancer, large polyps, and angiodysplasia are common 2, 5
• The presence of C. difficile may be coincidental to another bleeding source—dual pathology is common in elderly patients 2

Monitoring Strategy Going Forward

• After treating both the C. difficile and any identified bleeding source, monitor CBC every 3-6 months initially to detect recurrent iron deficiency 1
• If iron deficiency is confirmed and treated, continue iron therapy for three months after correction of anemia to replenish iron stores 2, 6