Microcytic Anemia With a "Normal" Ferritin in a Postmenopausal Woman
A 52-year-old woman presents with 6 months of fatigue and exertional breathlessness. Menopause occurred 2 years ago, and she has no history of heavy menstrual bleeding. She takes omeprazole 20 mg daily for reflux and ibuprofen 400 mg several times weekly for knee osteoarthritis. She eats red meat twice a week and drinks two cups of tea with meals. She has noticed no blood in the stool and has had no weight loss. Examination is unremarkable apart from pale conjunctivae and mild knee crepitus. Laboratory values: hemoglobin 10.1 g/dL, MCV 74 fL, ferritin 55 ng/mL, transferrin saturation 14%, CRP 22 mg/L, platelets 420,000/µL. A fecal immunochemical test done at a health fair last year was negative.
1. Does this patient have iron deficiency? Address the ferritin value directly.
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Yes. The ferritin of 55 ng/mL is the misleading number. Ferritin is an acute-phase reactant, so inflammation raises it independently of iron stores, and a ferritin in the "normal" reference range in a patient with a CRP of 22 mg/L does not exclude deficiency. The transferrin saturation of 14% is more informative: a saturation below 20% with a ferritin below 100 ng/mL in the setting of inflammation meets the accepted diagnostic threshold for iron deficiency. The microcytosis (MCV 74 fL), the thrombocytosis of 420,000/µL, and the low transferrin saturation are all consistent. Anemia of chronic inflammation alone would typically be normocytic with normal or high ferritin and a normal saturation.
Two features of the history are also clues: long-term omeprazole reduces gastric acid and impairs non-heme iron absorption, and tea taken with meals chelates iron. In a postmenopausal woman, occult blood loss remains the leading concern regardless of a negative fecal immunochemical test.
2. What is the next step in evaluation, and which commonly ordered test would be inadequate?
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The next step is to find the source. In a postmenopausal woman with documented iron deficiency, bidirectional endoscopy - upper endoscopy and colonoscopy - is indicated to exclude gastrointestinal malignancy and identify treatable sources such as angiodysplasia, erosions, or peptic ulcer disease. Add celiac serology (tissue transglutaminase IgA plus total IgA to exclude IgA deficiency), because celiac disease causes iron deficiency through proximal small bowel involvement and can be missed if duodenal biopsies are not obtained. Stop ibuprofen, which causes occult blood loss and mucosal injury, and substitute acetaminophen or topical therapy. Test for H. pylori if ulceration or gastritis is found.
Inadequate: repeating a fecal immunochemical test. A negative FIT does not exclude cancer in a patient with iron deficiency anemia, and a positive result merely confirms the need for the colonoscopy she already requires. Equally inadequate is a course of oral iron with a repeat hemoglobin in three months and no source evaluation, which delays diagnosis.
3. If oral iron is started, what limits its effectiveness here, and what should she expect?
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The pill is only part of the plan, and her circumstances blunt its effect. Omeprazole raises gastric pH and reduces iron absorption, and tea taken with meals chelates it further. Advise taking iron on an empty stomach with a vitamin C source, separated from tea, calcium, and ideally the proton pump inhibitor dose. Alternate-day dosing is preferable to twice daily: a single dose raises hepcidin for roughly 24 hours, and divided daily doses reduce fractional absorption.
Expected response: reticulocytosis within about 7 days, a hemoglobin rise of roughly 1 g/dL every 2-3 weeks, and normalization typically by 8-12 weeks. Continue iron for about three months after the hemoglobin normalizes to replete stores, then check ferritin and saturation. If she cannot tolerate oral iron, has ongoing blood loss, or fails to respond despite adherence, intravenous iron is appropriate. Failure to respond should prompt reassessment of the diagnosis, adherence, and ongoing loss rather than simply increasing the dose.