Management of Iron Deficiency Anemia with Ferritin 13 ng/mL
Start oral iron supplementation immediately with ferrous sulfate 200 mg (65 mg elemental iron) once daily, continue for 3 months after anemia correction to replenish iron stores, and initiate diagnostic workup including upper and lower GI endoscopy given the patient's age and elevated CRP. 1
Immediate Treatment Approach
Iron Replacement Therapy
Begin with ferrous sulfate 200 mg (65 mg elemental iron) once daily as first-line therapy, which is the most cost-effective and well-absorbed oral iron preparation 1, 2
If not tolerated, reduce to one tablet every other day rather than switching formulations immediately, as this improves tolerability while maintaining efficacy 1
Alternative oral preparations include ferrous gluconate or ferrous fumarate if ferrous sulfate causes intolerable side effects after trial of reduced dosing 1
Do not exceed 100 mg elemental iron per day in the context of elevated CRP, as inflammation may be present and higher doses provide no additional benefit while increasing side effects 1
Monitor hemoglobin response within 4 weeks—expect a rise of ≥10 g/L within 2 weeks if true iron deficiency 1
Continue iron therapy for 3 months after hemoglobin normalization to adequately replenish body iron stores 1
When to Consider Intravenous Iron
Reserve IV iron for intolerance to at least two different oral preparations, documented malabsorption, or if the patient requires urgent correction 1
In the presence of active inflammation (elevated CRP), oral absorption may be compromised; however, attempt oral therapy first unless there is evidence of ongoing blood loss requiring rapid correction 1
Diagnostic Workup Required
Essential Investigations
Upper GI endoscopy with small bowel biopsies to screen for celiac disease (found in 3-5% of IDA cases) and other upper GI pathology 1
Colonoscopy as the preferred lower GI investigation, or CT colonography if colonoscopy is not feasible given morbid obesity 1
Celiac disease serological screening (tissue transglutaminase antibodies with total IgA level) should be performed routinely 1
Urinalysis to exclude hematuria from urinary tract sources 1
Important Caveat About the Elevated CRP
The elevated CRP may falsely normalize ferritin levels, meaning true iron deficiency could exist even with ferritin values up to 100 ng/mL in inflammatory states 3
With ferritin 13 ng/mL, iron deficiency is confirmed regardless of inflammation, as this is well below the diagnostic threshold of <15 ng/mL (or <45 ng/mL in newer guidelines) 1
Consider checking transferrin saturation if ferritin results are ever equivocal in the context of inflammation 1, 3
Special Considerations for This Patient
At age 36, premenopausal status makes menorrhagia a common cause (responsible for 5-10% of IDA in menstruating women), but the elevated CRP and morbid obesity warrant full GI investigation regardless 1
Morbid obesity creates a pro-inflammatory state that can affect iron regulation through hepcidin, potentially contributing to functional iron deficiency 3
The combination of low ferritin (13 ng/mL) and elevated CRP suggests either true iron deficiency with concurrent inflammation or ongoing blood loss—both require investigation 3
Follow-Up Monitoring
Recheck hemoglobin and ferritin at 4 weeks to confirm response to oral iron (hemoglobin should rise by approximately 2 g/dL after 3-4 weeks) 1
After normalization, monitor every 3 months for the first year, then every 6-12 months thereafter to detect recurrence 1
Failure to respond (inadequate hemoglobin rise) indicates poor compliance, continued blood loss, malabsorption, or misdiagnosis—proceed with further investigation 1
If IDA recurs despite adequate initial treatment, further small bowel investigation with capsule endoscopy should be considered 1
Critical Pitfalls to Avoid
Do not defer iron replacement while awaiting endoscopy unless colonoscopy is imminent, as treatment should begin immediately 1
Do not use parenteral iron as first-line therapy in this stable patient without evidence of intolerance to oral preparations 1
Do not rely on fecal occult blood testing—it is insensitive and non-specific and should not guide investigation decisions 1
Do not stop investigating after finding one potential cause in a young patient with significant anemia; complete the bidirectional endoscopy as planned 1