What is the best course of action for a patient with mild microcytic anemia and low MCH and MCHC values?

Management of Microcytic Hypochromic Anemia with Low MCH and MCHC

Check serum ferritin immediately and initiate oral iron supplementation with ferrous sulfate 200 mg three times daily while investigating the underlying cause of iron loss. 1, 2

Immediate Diagnostic Workup

Your patient's lab values show:

• Borderline low MCV (80.2 fL) at the lower limit of normal
• Low MCH (24.9 pg) and low MCHC (31.0 g/dL) indicating hypochromia
• Normal hemoglobin (12.9 g/dL) for a female patient
• Normal RDW (12.5%) which is a critical distinguishing feature

Order serum ferritin as the single most specific test for iron deficiency: 1, 2

• Ferritin <15 μg/L confirms absent iron stores with 99% specificity 1
• Ferritin <30 μg/L indicates low body iron stores 1, 2
• Ferritin <45 μg/L warrants treatment and investigation, providing optimal sensitivity/specificity trade-off 1, 2
• Ferritin >150 μg/L essentially rules out absolute iron deficiency even with inflammation 1

Add transferrin saturation (TSAT) as it is more sensitive than hemoglobin alone for detecting iron deficiency 2, 3

The normal RDW is particularly important here: A low MCV with normal or near-normal RDW (≤14.0%) suggests thalassemia trait rather than iron deficiency, which typically shows RDW >14.0% 2, 3, 4. However, MCH is probably a more reliable marker than MCV for iron deficiency and is reduced in both absolute and functional iron deficiency 1.

Treatment Algorithm

Start empiric oral iron therapy immediately while awaiting ferritin results: 2, 3

• Ferrous sulfate 200 mg orally three times daily 2, 3, 5
• Continue for at least 3 months after anemia correction to replenish iron stores 2, 3
• If ferrous sulfate is not tolerated, switch to ferrous gluconate or ferrous fumarate 2, 3
• Add ascorbic acid (vitamin C) to enhance iron absorption 2, 3
• Do not crush or chew tablets 5

A therapeutic trial confirms the diagnosis: A hemoglobin rise ≥10 g/L within 2 weeks is highly suggestive of absolute iron deficiency, even if iron studies are equivocal 1, 2, 3. This is a strong recommendation from the British Society of Gastroenterology 1.

Investigation of Underlying Cause

In a female patient of reproductive age, investigate: 3

• Menstrual blood loss (quantity, duration, clots)
• Dietary iron intake (vegetarian diet, pica)
• Gastrointestinal blood loss (NSAID use, occult bleeding)
• Malabsorption (celiac disease, H. pylori, inflammatory bowel disease)

Consider gastrointestinal investigation at any level of anemia in the presence of iron deficiency, though the case is stronger with more severe degrees of anemia as they are more likely to have serious underlying GI pathology including colorectal cancer 1.

Alternative Diagnoses to Consider

If ferritin is normal or elevated and patient fails to respond to oral iron: 2, 3

1. Thalassemia trait - particularly likely given the normal RDW 2, 3

   • Order hemoglobin electrophoresis, especially if appropriate ethnic background (Mediterranean, Asian, African descent) 1
   • In thalassemia, MCV is typically reduced out of proportion to the level of anemia 1

2. Genetic disorders of iron metabolism (if unexplained microcytic anemia with increased TSAT) 3

   • Consider SLC11A2 defects
   • May require IV iron supplementation 2

3. X-linked sideroblastic anemia (ALAS2 defects) 2, 6

   • Initial treatment: pyridoxine (vitamin B6) 50-200 mg daily 2
   • Look for family history of anemia in males 6

4. Anemia of chronic disease - though less likely with low MCHC 1

Monitoring and Follow-up

Monitor response to therapy: 2, 3

• Recheck hemoglobin in 2 weeks - expect ≥10 g/L rise if iron deficiency 1, 2
• Expect hemoglobin increase of at least 2 g/dL within 4 weeks 2
• Monitor hemoglobin and red cell indices at 3-month intervals for 1 year, then after another year 2, 3
• Provide additional oral iron if hemoglobin or MCV falls below normal 2, 3

If no response to oral iron after 4 weeks: 2

• Consider IV iron if malabsorption present 2
• Evaluate for other causes including genetic disorders 2, 3
• Test for thalassemia if RDW remains normal 2

Critical Pitfalls to Avoid

Do not overlook combined deficiencies: Iron deficiency can coexist with B12 or folate deficiency, which may mask microcytosis 2, 3. The normal MCV here could represent combined iron deficiency with macrocytic process.

Do not assume normal hemoglobin excludes iron deficiency: This patient has hypochromia (low MCH/MCHC) with borderline low MCV, representing early iron deficiency before frank anemia develops 1, 7. Anisocytosis and increased percentage of microcytic cells are the first hematological abnormalities, occurring when transferrin saturation is <32% but hemoglobin is still normal 7.

Do not perform unnecessary GI investigation if thalassemia is confirmed: Hemoglobin electrophoresis is recommended in those with microcytosis and normal iron studies to prevent unnecessary GI investigation 1.