How should I evaluate and manage a 36-year-old premenopausal woman with iron-deficiency anemia (low ferritin, low serum iron, high total iron-binding capacity, low transferrin saturation) and light menstrual bleeding?

Evaluation and Management of Iron Deficiency Anemia with Light Menses

In a 36-year-old premenopausal woman with confirmed iron deficiency anemia and light menstrual bleeding, you must still investigate for gastrointestinal pathology—light menses does not exclude GI blood loss as the primary cause, and bidirectional endoscopy with coeliac screening remains essential. 1, 2

Why Light Menses Does Not Change the Diagnostic Approach

• Light menstrual bleeding substantially reduces the likelihood that menstruation is the sole cause of iron deficiency anemia in this patient. 3, 4 While heavy menstrual bleeding is the most common cause of IDA in premenopausal women, light menses should prompt investigation for alternative etiologies. 3, 5

• Gastrointestinal blood loss and malabsorption remain critical differential diagnoses even in premenopausal women with any pattern of menstruation. 1, 2 GI malignancy can present with IDA in the absence of specific symptoms, making urgent investigation mandatory. 1

• The British Society of Gastroenterology guidelines recommend bidirectional endoscopy for all adults with unexplained IDA, regardless of menstrual status. 1, 2 This is because dual pathology occurs in 10-15% of cases, and upper GI endoscopy reveals a cause in 30-50% of patients. 2

Essential Initial Investigations

• Perform coeliac disease screening immediately with tissue transglutaminase antibody (IgA type) plus total IgA level, as coeliac disease is found in 3-5% of IDA cases. 1, 2

• Conduct urinalysis or urine microscopy to exclude renal tract bleeding as a source of iron loss. 1, 2

• Verify iron deficiency with serum ferritin <30 ng/mL and transferrin saturation <20% (calculated as serum iron ÷ TIBC × 100). 6, 4 In the absence of inflammation, ferritin <30 ng/mL confirms absolute iron deficiency. 1, 6

• Measure C-reactive protein (CRP) to determine whether ferritin elevation is due to an acute-phase response, as inflammation can falsely elevate ferritin and mask true iron deficiency. 7, 6

Gastrointestinal Investigation Protocol

• Proceed with gastroscopy and colonoscopy as first-line investigations, even with light menses. 1, 2 This is non-negotiable in adults with unexplained IDA because GI malignancies can present this way. 1

• If bidirectional endoscopy is negative and IDA recurs or fails to respond to iron replacement therapy, perform capsule endoscopy to examine the small bowel. 1, 2 Capsule endoscopy is the preferred test for small bowel evaluation. 2

• CT or MR enterography may be considered if capsule endoscopy is contraindicated or unavailable. 2

Iron Replacement Strategy

• Do not defer iron replacement therapy while awaiting investigations, unless colonoscopy is imminent (within days). 1, 2 Starting treatment early improves symptoms and does not compromise diagnostic accuracy. 1

• Initiate oral iron with one tablet daily of ferrous sulfate 325 mg, ferrous fumarate, or ferrous gluconate. 2, 5 Alternate-day dosing may improve tolerability without compromising efficacy. 5

• Monitor hemoglobin response at 4 weeks; an increase ≥10 g/L within 2 weeks is highly suggestive of absolute iron deficiency, even if iron studies were equivocal. 1, 6

• If oral iron is not tolerated or ineffective after 4 weeks, switch to intravenous iron. 1, 5 IV iron has superior efficacy in patients with malabsorption, ongoing blood loss, or intolerance to oral preparations. 1, 5

Follow-Up Laboratory Monitoring

• Recheck complete blood count and iron parameters (ferritin, transferrin saturation) 4-8 weeks after completing iron replacement. 1 Do not check iron parameters within 4 weeks of IV iron administration, as circulating iron interferes with assays and produces spurious results. 1

• Target ferritin ≥50 ng/mL in the absence of inflammation to confirm adequate iron repletion. 1

• If hemoglobin does not increase after 4 weeks of oral iron, evaluate for ongoing blood loss, malabsorption, or functional iron deficiency (ferritin <100 ng/mL and transferrin saturation <20%). 1

Common Pitfalls to Avoid

• Do not assume light menses explains IDA without excluding GI pathology. 1, 2 This is a dangerous assumption that can delay diagnosis of serious conditions including malignancy. 1

• Do not rely on ferritin alone when it falls in the 30-100 ng/mL range; always calculate transferrin saturation, as functional iron deficiency can exist with normal-range ferritin. 6

• Do not dismiss the need for investigation based on age or sex; GI malignancy and coeliac disease occur in premenopausal women. 1, 2

• Do not stop iron therapy prematurely; continue until iron stores are repleted (ferritin ≥50 ng/mL), not just until hemoglobin normalizes. 1

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