What is the most likely diagnosis and appropriate next steps for an adult with a red‑blood‑cell count (3.43 ×10⁶/µL), hemoglobin (11.6 g/dL), hematocrit (34.1 %), mean corpuscular volume (normal), and mean corpuscular hemoglobin (33.8 pg)?

Normocytic Anemia with Elevated MCH

This presentation of low hemoglobin (11.6 g/dL), low RBC count (3.43 ×10⁶/µL), normal MCV, and elevated MCH (33.8 pg) most likely represents early vitamin B12 or folate deficiency that has not yet progressed to macrocytosis, and requires immediate measurement of serum B12 and folate levels. 1

Why This Is Not Iron Deficiency

• The elevated MCH (33.8 pg) essentially excludes typical iron deficiency anemia, as iron deficiency characteristically causes low MCH due to insufficient hemoglobin synthesis in red cells 2
• Iron deficiency causes both low MCV and low MCH, whereas this patient has normal MCV with high MCH—a pattern inconsistent with iron deficiency 3, 2
• MCH is actually more sensitive than MCV for detecting iron deficiency, so a high MCH makes iron deficiency extremely unlikely 2

Most Likely Diagnosis: Early B12/Folate Deficiency

• Early vitamin B12 or folate deficiency can present with anemia before macrocytosis develops, particularly when combined with other factors that suppress MCV 1
• Up to 35% of patients with untreated pernicious anemia have normal MCV in early stages 4
• The elevated MCH with normal MCV suggests a transition state where megaloblastic changes are beginning but not yet fully expressed 1
• Combined iron and B12/folate deficiency can mask macrocytosis, presenting with normal MCV but persistently elevated MCH—this is a critical diagnostic pitfall 1, 2

Immediate Diagnostic Workup Required

Order the following tests immediately:

• Serum vitamin B12 level to detect cobalamin deficiency 1
• Serum folate level to detect folate deficiency 1
• Complete iron panel (serum ferritin, transferrin saturation, serum iron, TIBC) to exclude combined deficiency 3, 2
• Reticulocyte count to assess bone marrow response and distinguish production defects from hemolysis 3, 1
• Peripheral blood smear to evaluate for hypersegmented neutrophils (pathognomonic for B12/folate deficiency) and other morphologic abnormalities 1

Additional Considerations

• If both B12 and folate are low, treat both simultaneously—never treat folate alone without excluding B12 deficiency first, as folate can mask B12 deficiency while allowing irreversible neurologic damage to progress 1
• The platelet count/MCH ratio can help identify combined deficiencies: a ratio >12.00 suggests coexisting iron and B12 deficiency 5
• Ferritin <30 μg/L confirms iron deficiency in the absence of inflammation, but ferritin is an acute phase reactant and can be falsely normal during inflammation 2, 6

Critical Pitfalls to Avoid

• Do not assume this is simple anemia of chronic disease based on the normal MCV—the elevated MCH demands investigation for nutritional deficiencies 1
• Do not empirically treat with iron without confirming iron deficiency, as the elevated MCH makes this diagnosis unlikely 1, 2
• Do not overlook combined deficiencies—iron deficiency can coexist with B12/folate deficiency, with the iron deficiency masking the macrocytosis but the MCH remaining elevated 1, 2
• Do not delay B12 measurement if folate deficiency is suspected, as treating folate alone without addressing B12 deficiency can precipitate subacute combined degeneration of the spinal cord 1

Expected Treatment Response

• Once the specific deficiency is identified and treated, expect hemoglobin to increase by 1-2 g/dL every 2-4 weeks 1, 6
• Reticulocyte count should increase within 1 week of starting appropriate therapy, indicating bone marrow response 1
• Repeat CBC after 4-8 weeks to confirm hemoglobin rise and assess treatment adequacy 1