What is the diagnosis and recommended treatment for a 64‑year‑old woman with a hematocrit of 35.8%, elevated red cell distribution width, low mean corpuscular hemoglobin, low mean corpuscular hemoglobin concentration, and mild monocytosis, eosinophilia, and basophilia?

Diagnosis: Iron Deficiency Anemia

This 64-year-old woman has iron deficiency anemia, characterized by microcytic hypochromic red cells (low MCH 22.9 pg, low MCHC 29.6 g/dL) with elevated RDW (18.2%), indicating a heterogeneous red cell population typical of iron deficiency. 1

Laboratory Interpretation

The combination of low MCV (implied by low MCH) with RDW >14.0% strongly indicates iron deficiency anemia rather than thalassemia, which typically presents with RDW ≤14.0%. 1, 2

• MCH is more reliable than MCV for detecting iron deficiency because it is less dependent on storage conditions and counting equipment, and decreases in both absolute and functional iron deficiency. 1
• The hematocrit of 35.8% represents moderate anemia in an adult woman (normal ≥36%). 3
• The mild monocytosis (10.7%), eosinophilia (3.7%), and basophilia (1.8%) are nonspecific findings that do not alter the primary diagnosis. 1

Required Diagnostic Workup

Before initiating treatment, you must obtain serum ferritin and transferrin saturation to confirm iron deficiency and guide therapy. 1, 2

• Serum ferritin <30 μg/L confirms iron deficiency in the absence of inflammation; ferritin <100 μg/L indicates iron deficiency when inflammation is present. 1
• Transferrin saturation <16–20% confirms insufficient circulating iron for erythropoiesis. 1
• Measure C-reactive protein (CRP) concurrently because ferritin is an acute-phase reactant that can be falsely elevated in inflammatory, infectious, malignant, or hepatic conditions. 2

Mandatory Investigation for Source of Iron Loss

In a 64-year-old woman with confirmed iron deficiency anemia, gastrointestinal evaluation is mandatory even if menstrual bleeding appears explanatory, because occult GI malignancy is a critical concern in this age group. 2

• Both upper endoscopy with duodenal biopsies AND colonoscopy must be performed to exclude gastrointestinal malignancy, which is the most common cause of iron deficiency in post-menopausal women. 2
• Upper endoscopy with duodenal biopsies is required to exclude celiac disease, which accounts for 2–3% of iron deficiency anemia cases. 1, 2
• Colonoscopy is high-yield for detecting colonic carcinoma, adenomatous polyps, and angiodysplasia in older adults. 2
• Heavy menstrual bleeding should be assessed if the patient is still menstruating, but this does not eliminate the need for GI evaluation. 2

Treatment Algorithm

Immediate Therapy

Initiate oral iron supplementation immediately while the diagnostic workup proceeds. 2

• First-line treatment is ferrous sulfate 200 mg (65 mg elemental iron) three times daily for at least three months after correction of anemia to replenish iron stores. 2
• Alternative formulations include ferrous gluconate or ferrous fumarate if ferrous sulfate is not tolerated; ascorbic acid can be added to enhance iron absorption. 2

Expected Response and Monitoring

• A hemoglobin rise ≥10 g/L (≥1 g/dL) within 2 weeks confirms iron deficiency diagnosis. 1, 2
• If the patient fails to respond to oral iron within 2–4 weeks, consider non-compliance, ongoing blood loss, malabsorption, or true intolerance to oral preparations. 2

Second-Line Therapy for Treatment Failure

If malabsorption is confirmed or oral iron is not tolerated, switch to intravenous iron (iron sucrose or iron gluconate) with an expected hemoglobin increase of at least 2 g/dL within 4 weeks. 1, 2, 4

• Intravenous iron sucrose can be administered as 200 mg over 2–5 minutes five times within 14 days, or two 500 mg infusions on Day 1 and Day 14 over 3.5–4 hours. 4

Long-Term Monitoring

• Monitor hemoglobin concentration and red cell indices at three-monthly intervals for one year, then after a further year. 2
• Provide additional oral iron if hemoglobin or MCV falls below normal. 2

Critical Pitfalls to Avoid

• Do not attribute iron deficiency anemia in a 64-year-old woman solely to inadequate dietary intake or menstrual loss; occult gastrointestinal blood loss from malignancy must be excluded. 2
• Do not rely on ferritin alone when inflammation is present; add transferrin saturation to confirm iron deficiency. 1
• Do not overlook combined deficiencies—iron deficiency may coexist with vitamin B12 or folate deficiency, suggested by elevated RDW with normal MCV. 1, 5
• Do not assume all microcytic anemia is iron deficiency; if iron studies are normal, order hemoglobin electrophoresis to exclude thalassemia trait. 1, 2
• Do not delay gastrointestinal investigation while treating with iron; both should proceed simultaneously. 2