What conditions can cause persistent iron‑deficiency anemia in a woman who receives monthly intravenous iron, eats a diet rich in red meat, and does not have heavy menstrual bleeding?

Persistent Iron-Deficiency Anemia Despite IV Iron: Key Underlying Conditions

In a woman with persistent iron-deficiency anemia despite monthly IV iron, adequate dietary intake, and no heavy menstrual bleeding, you must systematically investigate for occult gastrointestinal blood loss, malabsorption disorders (particularly celiac disease and atrophic gastritis), and hereditary iron-refractory iron deficiency anemia (IRIDA).

Primary Diagnostic Approach

1. Gastrointestinal Blood Loss (Most Common)

Even without overt bleeding, occult GI blood loss is the leading cause of refractory IDA. Bidirectional endoscopy (gastroscopy and colonoscopy) is the cornerstone investigation 1, 2. Studies show approximately one-third of adults over 50 with unexplained IDA have underlying GI abnormalities, with one-third of these being malignancies 2.

Key lesions to identify:

• Upper GI: gastric/duodenal ulcers, gastric cancer, angiodysplasia
• Lower GI: colon cancer (7 times more common than upper GI cancer), polyps, inflammatory bowel disease, angiodysplasia
• Small bowel sources (if bidirectional endoscopy negative): capsule endoscopy should be considered if red flags present (weight loss, abdominal pain, elevated CRP) 1, 3

2. Malabsorption Syndromes

Celiac disease screening is mandatory before or alongside endoscopy 1, 3. Test with:

• Tissue transglutaminase antibody (IgA type)
• Total IgA level (to exclude IgA deficiency)

Atrophic gastritis causes iron malabsorption by reducing gastric acid production, which is essential for iron absorption 3. This is particularly relevant given the patient's lack of response to oral iron historically.

Other malabsorption causes:

• Prior bariatric surgery (gastric bypass severely impairs iron absorption) 3, 4
• Inflammatory bowel disease (Crohn's disease affecting duodenum/jejunum) 1
• Helicobacter pylori infection (can cause both blood loss and malabsorption) 1

3. Hereditary Iron-Refractory Iron Deficiency Anemia (IRIDA)

IRIDA should be suspected when IV iron provides only partial or temporary response 5. This rare genetic condition is caused by TMPRSS6 gene mutations leading to elevated hepcidin levels, which block iron absorption and utilization even with IV supplementation 5.

Diagnostic clues for IRIDA:

• Microcytic anemia since childhood or adolescence
• Persistently low transferrin saturation despite IV iron
• Elevated or inappropriately normal hepcidin levels
• Family history of refractory anemia
• Genetic testing confirms TMPRSS6 variants 5

Critical Pitfalls to Avoid

Monthly IV iron may mask ongoing blood loss rather than correct the underlying problem. If hemoglobin stabilizes only temporarily after each infusion, this strongly suggests continuous blood loss exceeding iron replacement capacity 1.

Don't assume adequate absorption from diet alone. Even with high red meat intake, conditions like atrophic gastritis, celiac disease, or chronic inflammation can prevent iron absorption. The presence of inflammation (check CRP) can also sequester iron through hepcidin elevation, creating functional iron deficiency 4.

Age matters for investigation intensity. While guidelines suggest bidirectional endoscopy may not be required in premenopausal women under 40 without risk factors 3, this patient's refractory nature despite IV iron warrants full investigation regardless of age 2.

Algorithmic Workup

1. Verify true iron deficiency: Check ferritin (if <30 ng/mL confirms deficiency; if 30-100 ng/mL with inflammation, check fasting transferrin saturation <20%) 1

2. Screen for celiac disease: Tissue transglutaminase IgA + total IgA 1, 3

3. Perform bidirectional endoscopy with biopsies from stomach (assess for atrophic gastritis, H. pylori) and duodenum (assess for celiac disease even if serology negative) 1, 2

4. If endoscopy negative and anemia persists: Consider capsule endoscopy for small bowel evaluation, particularly if any red flags present 1

5. Consider IRIDA: If all GI workup negative and patient has lifelong microcytic anemia with poor IV iron response, pursue genetic testing for TMPRSS6 mutations 5

6. Assess for functional iron deficiency: Check inflammatory markers (CRP, ESR) and consider underlying chronic inflammatory conditions that elevate hepcidin 4

Treatment Adjustments Based on Findings

If ongoing blood loss identified: Treat the source (e.g., anticoagulant adjustment, PPI for ulcers, IBD therapy). IV iron frequency may need to increase to match losses 1.

If malabsorption confirmed: IV iron becomes the primary route; oral supplementation is futile 1, 4. Treat underlying condition (gluten-free diet for celiac, B12 for atrophic gastritis).

If IRIDA diagnosed: Higher and more frequent IV iron doses may be needed, with recognition that complete normalization may not be achievable 5. Avoid futile oral iron trials.

The key principle: persistent IDA despite IV iron is never normal and always warrants investigation for an underlying cause 1, 2. The monthly IV iron requirement itself signals either ongoing losses or a fundamental problem with iron utilization that must be identified and addressed.