Could Chronic Bleeding Be the Cause?
Yes, chronic bleeding is a highly plausible cause of microcytic anemia even with normal ferritin levels, particularly in the context of inflammatory conditions that can mask iron deficiency. 1
Understanding the Paradox of Normal Ferritin with Microcytic Anemia
The key issue here is that ferritin is an acute-phase reactant that becomes falsely elevated during inflammation, potentially masking true iron deficiency. 1 In patients without inflammation, a ferritin <30 mcg/L defines iron deficiency, but in the presence of inflammation, ferritin levels up to 100 mcg/L may still indicate iron deficiency. 1
Critical Diagnostic Considerations
Transferrin saturation <16% is the critical parameter to assess - if this is low despite "normal" ferritin, it strongly suggests functional iron deficiency from chronic blood loss. 1
Check for inflammatory markers (CRP, ESR) - if elevated, your ferritin threshold for diagnosing iron deficiency must be raised to 100 mcg/L rather than the standard 30 mcg/L. 1
An elevated red cell distribution width (RDW) can unmask hidden iron deficiency even when microcytosis coexists with other factors that might normalize the MCV. 1, 2
The Chronic Bleed Scenario
Chronic gastrointestinal bleeding is found in 60-70% of patients with iron deficiency anemia who undergo endoscopy. 3 This makes it one of the most common culprits for microcytic anemia.
Why the Elevated B12 Doesn't Rule Out Bleeding
The elevated vitamin B12 (cobalamin) is a red herring - it does not exclude chronic bleeding as the cause of microcytic anemia. 4
Elevated B12 can occur in various conditions including liver disease, myeloproliferative disorders, or recent supplementation, and does not protect against or exclude iron deficiency from blood loss. 4
Diagnostic Algorithm for This Patient
First-line assessment:
- Measure transferrin saturation - if <16%, this confirms iron deficiency regardless of ferritin level. 1
- Check inflammatory markers (CRP) - if elevated, interpret ferritin in this context. 1
- Evaluate RDW - if elevated, this supports coexisting iron deficiency. 2
Second-line investigation:
- Assess for occult blood loss in stool - this is essential in all patients with unexplained microcytic anemia. 1
- Consider endoscopic evaluation if iron deficiency is confirmed, as GI bleeding is the most common source. 3
Common Pitfall to Avoid
Never assume normal ferritin excludes iron deficiency in a patient who may have any inflammatory condition (infection, autoimmune disease, malignancy, chronic disease). 1 The combination of microcytic anemia with normal ferritin should prompt you to look at transferrin saturation and inflammatory markers before dismissing chronic bleeding as the cause. 1
Treatment Implications
If iron deficiency from chronic bleeding is confirmed, identify and address the bleeding source before or concurrent with iron replacement. 1
Iron supplementation alone without stopping the bleeding will result in treatment failure. 5
Parenteral iron may be necessary if ongoing GI losses exceed oral replacement capacity. 5