What is the diagnosis and treatment for a patient with microcytic anemia and laboratory values indicating low hemoglobin, low hematocrit, and abnormal red blood cell indices?

Microcytic Anemia with Elevated RDW: Iron Deficiency Until Proven Otherwise

Based on your laboratory values (MCV 59.4, MCH 18.9, RDW 18.7%), this is iron deficiency anemia, and you should start oral ferrous sulfate 324 mg (65 mg elemental iron) one to three times daily for at least three months after hemoglobin normalizes. 1, 2

Diagnostic Interpretation

Your patient's lab pattern is pathognomonic for iron deficiency:

• Low MCV (59.4) combined with elevated RDW (18.7%) strongly indicates iron deficiency anemia, as this combination distinguishes it from thalassemia minor, which typically presents with low MCV but RDW ≤14.0% 1, 2
• The hemoglobin of 12.4 g/dL with hematocrit 39% confirms mild-to-moderate anemia 2
• The markedly low MCH (18.9) further supports iron deficiency, as MCH is more reliable than MCV for detecting both absolute and functional iron deficiency 1

Confirmatory Testing Required

Before initiating treatment, obtain these specific tests:

• Serum ferritin is the single most useful diagnostic marker: <15 μg/L indicates absent iron stores, <30 μg/L indicates low stores, and <45 μg/L is the optimal cut-off for clinical diagnosis 1, 2
• Transferrin saturation (TSAT) should be measured, as it is more sensitive than hemoglobin alone for detecting iron deficiency 1, 2
• If ferritin is normal or elevated despite microcytic anemia, add TSAT to detect functional iron deficiency masked by inflammation 1

First-Line Treatment Protocol

Oral ferrous sulfate 324 mg (65 mg elemental iron) taken one to three times daily for at least three months after hemoglobin correction is the standard first-line therapy 1, 2:

• Alternative formulations (ferrous gluconate or ferrous fumarate) can be used if gastrointestinal side effects are intolerable 1, 2
• Adding ascorbic acid (vitamin C) enhances iron absorption 1, 2
• Continue treatment for at least 3 months after anemia correction to replenish iron stores 1, 2

Expected Response and Monitoring

A good response is defined as hemoglobin rise ≥10 g/L (≥1 g/dL) within 2 weeks, which confirms iron deficiency 1, 2:

• Expect hemoglobin increase of at least 2 g/dL within 4 weeks 1, 2
• Monitor hemoglobin, MCV, and iron studies at 2 weeks, 4 weeks, 3 months, then every 3 months for the first year, then annually 1, 2
• Provide additional oral iron if hemoglobin or MCV falls below normal during follow-up 1, 2

Critical Next Step: Identify the Source of Blood Loss

In adults with confirmed iron deficiency, you must investigate the source of iron loss 1:

• Men with Hb <110 g/L or non-menstruating women with Hb <100 g/L warrant fast-track gastrointestinal referral 1
• Evaluate specifically for gastrointestinal blood loss (melena, hematochezia, occult bleeding) 1
• Screen for celiac disease if malabsorption is suspected 1
• Consider menstrual history in premenopausal women 3

When Oral Iron Fails

If the patient fails to respond to oral iron therapy after 4 weeks:

• Consider intravenous iron if malabsorption is present, with expected hemoglobin increase of at least 2 g/dL within 4 weeks 1
• Evaluate for genetic disorders of iron metabolism, particularly IRIDA (TMPRSS6 mutations), which presents with very low TSAT, low-to-normal ferritin, and resistance to oral iron 4, 1, 2
• For IRIDA, intravenous iron (iron sucrose or iron gluconate) is required, as oral iron is typically ineffective 4, 2
• Test for thalassemia if RDW normalizes or is near normal despite persistent microcytosis 1

Common Pitfalls to Avoid

• Do not assume all microcytic anemia is iron deficiency: anemia of chronic disease, thalassemia, and sideroblastic anemia must be differentiated to avoid unnecessary iron therapy 1
• Do not overlook combined deficiencies, such as iron deficiency coexisting with B12 or folate deficiency 1
• Ferritin can be falsely elevated by inflammation, making it appear normal despite true iron deficiency; add TSAT in these cases 1
• Hemoglobin electrophoresis should be ordered if microcytosis persists with normal iron studies, appropriate ethnic background, or MCV disproportionately low relative to degree of anemia 1