What does a low Mean Corpuscular Hemoglobin (MCH) and Mean Corpuscular Hemoglobin Concentration (MCHC) indicate?

Low MCH and MCHC Primarily Indicate Iron Deficiency Anemia

Low Mean Corpuscular Hemoglobin (MCH) and Mean Corpuscular Hemoglobin Concentration (MCHC) most commonly indicate iron deficiency anemia, which requires further investigation and treatment to prevent morbidity and mortality. 1

Understanding MCH and MCHC

MCH and MCHC are red blood cell indices that provide important diagnostic information:

• MCH (Mean Corpuscular Hemoglobin): Measures the average amount of hemoglobin in each red blood cell
• MCHC (Mean Corpuscular Hemoglobin Concentration): Measures the average concentration of hemoglobin in a given volume of red blood cells

Clinical Significance of Low MCH and MCHC

Primary Causes

1. Iron Deficiency Anemia (Most Common)

   • MCH is considered a more reliable marker of iron deficiency than MCV (Mean Corpuscular Volume) 1
   • MCH may be more sensitive for detecting early iron deficiency than MCV 1
   • Low MCHC typically appears in the final stage of iron deficiency when hemoglobin falls below 9 g/dL 2

2. Stages of Iron Deficiency 2

   • Early stage: Anisocytosis (variation in cell size) and microcytosis appear first, with normal hemoglobin
   • Intermediate stage: MCV and MCH decline, hemoglobin becomes subnormal but remains above 9 g/dL
   • Advanced stage: MCHC becomes low, hemoglobin drops below 9 g/dL

Other Potential Causes

Low MCH and MCHC can also be seen in:

• Hemoglobinopathies (e.g., thalassemia) 1
• Sideroblastic anemia 1
• Anemia of chronic disease (in some cases) 1
• Chronic inflammatory conditions (including chronic periodontal disease) 3

Diagnostic Approach

When low MCH and MCHC are identified:

1. Confirm iron deficiency with iron studies 1, 4

   • Serum ferritin (most specific test for iron deficiency)
   • Transferrin saturation
   • Serum iron levels
   • Total iron-binding capacity

2. Consider additional testing if diagnosis remains unclear:

   • Complete blood count with red cell indices
   • Peripheral blood smear examination
   • Reticulocyte count
   • Hemoglobin electrophoresis (particularly in patients with microcytosis and normal iron studies) 1

3. Evaluate for underlying causes of iron deficiency:

   • Blood loss (gastrointestinal, menstrual)
   • Malabsorption
   • Increased iron requirements (pregnancy)
   • Poor dietary intake

Clinical Pearls and Pitfalls

Important Considerations

• MCH is less dependent on storage and counting machine variables compared to MCV 1
• MCH changes are seen in both absolute and functional iron deficiency 1
• The diagnostic accuracy of MCH and MCHC for iron deficiency is fairly good (area under ROC curve of 0.67 for MCH and 0.71 for MCHC) 5

Common Pitfalls

• Overlooking iron deficiency when ferritin appears normal due to concurrent inflammation 1, 4
• Failing to investigate the cause of anemia, even if mild 4
• Missing multiple concurrent causes of anemia 4
• Neglecting to consider that microcytosis and hypochromia lose sensitivity for iron deficiency in the presence of chronic disease, thalassaemia, or vitamin B12/folate deficiency 1

Treatment Implications

If iron deficiency is confirmed:

• Oral iron therapy is first-line treatment (100-200 mg elemental iron daily) 4
• Intravenous iron may be considered if oral iron is not tolerated or ineffective 4
• Monitor response with repeat CBC in 4-8 weeks (expect hemoglobin increase of at least 2 g/dL) 4
• A good response to iron therapy (Hb rise ≥10 g/L within 2 weeks) is highly suggestive of absolute iron deficiency 1

By properly identifying and addressing the underlying cause of low MCH and MCHC, clinicians can effectively prevent the morbidity and mortality associated with untreated iron deficiency anemia.