What is the diagnosis and treatment for a patient with hypochromic microcytic anemia (low hemoglobin, normal hematocrit, low mean corpuscular volume) and elevated red cell distribution width?

Diagnosis: Iron Deficiency Anemia

This presentation of low hemoglobin, normal hematocrit, low MCV, and high RDW is diagnostic of iron deficiency anemia (IDA), and you should immediately confirm with serum ferritin and initiate oral iron supplementation while investigating for the source of blood loss. 1, 2

Why This Is Iron Deficiency Anemia

The combination of microcytosis (low MCV) with elevated RDW is the key distinguishing feature that strongly points to iron deficiency rather than thalassemia trait 1, 2. Here's the diagnostic logic:

• Elevated RDW with low MCV creates a highly specific pattern for IDA because iron deficiency produces red blood cells of varying sizes (anisocytosis), whereas thalassemia trait produces uniformly small cells with normal RDW 1, 3
• The normal hematocrit with low hemoglobin suggests early or evolving anemia where red cell count may still be relatively preserved 4
• Microcytic hypochromic pattern (low MCV, low MCH, low MCHC) is the hallmark of iron deficiency according to the American Gastroenterological Association 1

Confirmatory Testing

Order serum ferritin immediately as the single most useful confirmatory test 1:

• Ferritin <30 μg/L in the absence of inflammation confirms iron deficiency 1, 2
• If ferritin is equivocal (30-100 μg/L), check transferrin saturation; <20% supports iron deficiency 1
• Also obtain CRP to assess for inflammation that might elevate ferritin 2
• Consider reticulocyte count to confirm appropriate bone marrow response 2, 5

Immediate Treatment

Start oral iron supplementation immediately upon confirming iron deficiency—do not wait for source identification 1, 2:

• Initiate standard oral iron therapy (ferrous sulfate 325 mg daily or every other day) 1
• Recheck complete blood count in 2 weeks; a hemoglobin rise ≥10 g/L confirms iron deficiency even if iron studies were equivocal 1
• Continue treatment for 3-6 months after hemoglobin normalizes to replenish iron stores 1
• Failure to respond suggests ongoing blood loss, malabsorption, or incorrect diagnosis 1

Mandatory Investigation for Blood Loss Source

All patients with confirmed IDA require gastrointestinal evaluation to identify the source of blood loss, even young menstruating women 1:

History to Obtain:

• Menstrual history: Quantify blood loss (number of pads/tampons per day, duration, presence of clots) 1
• Medication use: Document NSAIDs, aspirin, anticoagulants 1
• Dietary assessment: Evaluate iron intake, though inadequate diet alone should not preclude GI investigation 1
• GI symptoms: Abdominal pain, change in bowel habits, dysphagia (though symptoms poorly correlate with findings) 1

Endoscopic Evaluation Algorithm:

• Upper endoscopy with small bowel biopsies to screen for celiac disease (present in 2-3% of IDA patients) 1
• Colonoscopy should follow unless upper endoscopy reveals cancer or celiac disease 1
• For adult men and post-menopausal women, both upper and lower GI endoscopy should be performed to exclude malignancy 2
• A source of gastrointestinal bleeding is found in 60-70% of patients with IDA referred for endoscopy 4

Critical Pitfalls to Avoid

• Do not assume thalassemia trait based solely on microcytosis without checking ferritin and RDW—the elevated RDW essentially rules out thalassemia 2, 5
• Do not skip GI investigation in young women by attributing anemia solely to menstruation; the threshold for investigation should be low with any degree of anemia in the presence of confirmed iron deficiency 1
• Do not overlook combined deficiencies (e.g., iron and B12), which may result in a normal MCV despite abnormal RDW 2
• Do not delay iron supplementation while waiting for endoscopy results 1