What causes low MCH and how is it treated?

Causes and Treatment of Low Mean Corpuscular Hemoglobin (MCH)

Low MCH is primarily caused by iron deficiency, but can also result from thalassemia, anemia of chronic disease, or sideroblastic anemia, with iron supplementation being the mainstay of treatment for iron deficiency-related low MCH. 1

Causes of Low MCH

Primary Causes:

1. Iron Deficiency Anemia (Most Common)

   • Results from:
     • Blood loss (gastrointestinal bleeding, menstruation)
     • Increased iron demand (pregnancy)
     • Insufficient dietary intake
     • Impaired iron absorption 2
   • Characterized by:
     • Low serum ferritin (<15 μg/L confirms deficiency)
     • Low transferrin saturation
     • Low serum iron
     • Raised total iron-binding capacity 1

2. Thalassemia

   • Genetic disorder affecting hemoglobin production
   • MCV typically reduced out of proportion to anemia level
   • Normal or high ferritin levels despite low MCH 1

3. Anemia of Chronic Disease

   • Associated with chronic inflammatory conditions
   • Presents with low MCH but often normal/high ferritin
   • Low transferrin saturation 3

4. Sideroblastic Anemia

   • Rare disorder of heme synthesis
   • Can present with low MCH despite normal iron stores 1

5. Iron-Refractory Iron Deficiency Anemia (IRIDA)

   • Rare genetic disorder due to TMPRSS6 mutations
   • Causes iron deficiency resistant to oral iron therapy 3, 2

Diagnostic Approach:

• Complete blood count with MCH and MCV
• Serum ferritin (most specific test for iron deficiency)
• Transferrin saturation
• Serum iron and total iron-binding capacity
• Consider hemoglobin electrophoresis if thalassemia suspected 1, 3

Note: MCH is considered a more reliable marker of iron deficiency than MCV as it is less dependent on storage and counting machine used. It may also be more sensitive for detecting iron deficiency. 1

Treatment of Low MCH

For Iron Deficiency:

1. Oral Iron Supplementation (First-line)

   • Ferrous sulfate 200 mg three times daily (65 mg elemental iron per dose)
   • Continue for 3 months after normalization of hemoglobin to replenish stores 3
   • Add ascorbic acid to enhance absorption in resistant cases 3

2. Intravenous Iron (When oral therapy is ineffective or not tolerated)

   • Indicated for:
     • Malabsorption
     • Losses exceeding oral replacement capacity
     • Intolerance to oral preparations
     • Need for rapid replenishment 4
   • Dosing based on body weight and hemoglobin level 1
   • Monitor for adverse reactions (allergic reactions, hypophosphatemia) 2

3. Treat Underlying Causes

   • Investigate and address sources of blood loss
   • Manage chronic conditions contributing to anemia 2

For Other Causes:

1. Thalassemia

   • Genetic counseling
   • Supportive care
   • Transfusions if severe 3

2. Anemia of Chronic Disease

   • Treat underlying inflammatory condition
   • Consider erythropoiesis-stimulating agents in specific cases 1, 3

3. Sideroblastic Anemia

   • Pyridoxine supplementation may help some forms
   • Avoid excessive iron supplementation 3

Monitoring and Follow-up

• Repeat CBC in 2-4 weeks to assess response to treatment
• Monitor ferritin and transferrin saturation
• Target hemoglobin rise of ≥10 g/L within 2 weeks indicates good response to iron therapy 1
• For IV iron therapy, monitor ferritin levels with target not exceeding 500 μg/L 3

Special Considerations

• Pregnancy: Higher iron requirements (30 mg/day, increasing to 60-120 mg/day for anemia) 3
• Heart Failure: IV iron may improve outcomes in patients with iron deficiency and heart failure 1, 2
• Chronic Kidney Disease: May require erythropoiesis-stimulating agents in addition to iron 3
• Inflammatory Bowel Disease: IV iron may be more effective than oral iron 3

Common Pitfalls to Avoid

1. Relying solely on MCV or MCH for diagnosis without confirming iron status
2. Misinterpreting ferritin levels in inflammatory states (may be falsely normal/elevated)
3. Failing to investigate underlying causes of iron deficiency
4. Not continuing iron therapy long enough to replenish stores
5. Overlooking genetic causes like thalassemia or IRIDA in resistant cases 1, 3