What is the likely diagnosis and next management for an adult with low mean corpuscular hemoglobin, low mean corpuscular hemoglobin concentration, and elevated red cell distribution width?

Diagnosis and Management of Hypochromic Microcytic Anemia with Elevated RDW

Most Likely Diagnosis

The laboratory findings of low MCH (26.1 pg), low MCHC (30.3 g/dL), and elevated RDW (15.8) are highly suggestive of iron deficiency anemia and require immediate confirmation with iron studies. 1, 2

Immediate Next Steps

Order a complete iron panel immediately, including serum ferritin, transferrin saturation, and C-reactive protein (CRP). 1, 2 These values are essential because:

• MCH is a more reliable marker of iron deficiency than MCV because it is less dependent on storage conditions and laboratory equipment, and decreases in both absolute and functional iron deficiency 1, 2
• Low MCHC indicates hypochromia (red blood cells contain less hemoglobin than normal), which strongly suggests iron deficiency 1, 2
• Elevated RDW with low MCH/MCHC specifically indicates iron-deficient erythropoiesis, even before frank anemia fully develops, with a sensitivity of 72% for detecting iron deficiency 2

Interpreting Iron Studies

Without Inflammation (CRP normal):

• Serum ferritin <15 μg/L confirms absent iron stores 1
• Ferritin <30 μg/L indicates low body iron stores and confirms iron deficiency 1, 2
• Transferrin saturation <16-20% supports iron deficiency 1, 2

With Inflammation (elevated CRP):

• Ferritin up to 45-100 μg/L may still indicate iron deficiency because ferritin is an acute-phase reactant that can be falsely elevated 1, 2
• Ferritin >150 μg/L makes absolute iron deficiency unlikely even with inflammation 1
• If ferritin is 30-100 μg/L with inflammation, consider a combination of true iron deficiency and anemia of chronic disease 1, 2

If Iron Deficiency is Confirmed

Initiate Treatment:

• Start oral iron supplementation with ferrous sulfate 325 mg (65 mg elemental iron) once daily between meals 2
• Expect hemoglobin increase of approximately 1-2 g/dL every 2-4 weeks 2
• A rise in hemoglobin ≥10 g/L (≈1 g/dL) within 2 weeks strongly confirms absolute iron deficiency, even if initial iron studies were equivocal 1

Investigate the Underlying Cause:

• All adult men and postmenopausal women with confirmed iron deficiency require gastrointestinal evaluation to exclude malignancy, regardless of anemia severity 1, 2
• In premenopausal women, assess menstrual blood loss, but do not assume this is the sole cause without excluding GI pathology if symptoms warrant 1
• Consider dietary history, NSAID use, previous gastrectomy, and celiac disease 1

Follow-up:

• Check hemoglobin, reticulocytes, and iron studies after 4-8 weeks of therapy 2
• Continue iron supplementation for 3-6 months after hemoglobin normalizes to replenish iron stores 2

If Iron Studies Are Normal Despite Low MCH/MCHC

Consider Alternative Diagnoses:

• Obtain hemoglobin electrophoresis to evaluate for thalassemia trait, especially in individuals of Mediterranean, African, or Southeast Asian descent 1, 2
• In thalassemia trait, MCV is typically reduced disproportionately to the degree of anemia, and the red cell count is usually elevated 1
• Consider anemia of chronic disease—assess for underlying inflammatory conditions 1, 2
• Consider sideroblastic anemia in refractory cases 1

Common Pitfalls to Avoid

• Do not rely on MCV alone, as iron deficiency can present with normal MCV in early stages, and MCH may be more sensitive 1, 2
• Do not dismiss apparently normal ferritin values in inflammatory states—use the higher cutoff of 45-100 μg/L depending on inflammation severity 1, 2
• Do not assume dietary insufficiency or menstrual losses are the sole cause without investigating for GI blood loss, as this can delay diagnosis of serious pathology like colorectal cancer 1
• Do not forget that both microcytosis and hypochromia lose sensitivity for iron deficiency in the presence of chronic disease, thalassemia, or vitamin B12/folate deficiency 1

When to Consider Parenteral Iron

• Patient is intolerant to oral iron 2
• Poor response to oral iron after adequate trial 2
• Severe anemia requiring rapid correction 2
• Malabsorption (e.g., celiac disease, inflammatory bowel disease) 1