What are MCH (Mean Corpuscular Hemoglobin) and MCHC (Mean Corpuscular Hemoglobin Concentration) on a Complete Blood Count (CBC) test?

MCH and MCHC on CBC: Key Red Blood Cell Indices

MCH (Mean Corpuscular Hemoglobin) and MCHC (Mean Corpuscular Hemoglobin Concentration) are essential red blood cell indices on a Complete Blood Count that provide critical information about hemoglobin content within red blood cells, helping to diagnose and classify various types of anemia.

Definitions and Calculations

• MCH (Mean Corpuscular Hemoglobin):

  • Measures the average amount of hemoglobin in each red blood cell, expressed in picograms (pg)
  • Calculated as: Total hemoglobin ÷ Red blood cell count
  • Normal range: Typically 27-33 pg 1

• MCHC (Mean Corpuscular Hemoglobin Concentration):

  • Measures the average concentration of hemoglobin in a given volume of packed red blood cells, expressed in g/dL
  • Calculated as: MCH ÷ MCV (Mean Corpuscular Volume) or Hemoglobin ÷ Hematocrit
  • Normal range: Typically 32-36 g/dL 1, 2

Clinical Significance

Diagnostic Value in Anemia Classification

MCH and MCHC are used alongside MCV to classify anemias:

1. Low MCH and MCHC (Hypochromic):

   • Strongly indicates iron deficiency anemia 1
   • May indicate thalassemia
   • Can occur in anemia of chronic disease 1

2. Normal MCH and MCHC (Normochromic):

   • Typical in anemia of chronic disease/inflammation
   • Common in acute blood loss
   • Seen in renal insufficiency anemia 1

3. High MCHC:

   • Physiologically impossible beyond certain limits due to hemoglobin solubility constraints
   • May indicate certain hemolytic anemias
   • Can be an artifact requiring critical evaluation of the peripheral smear 2

Role in Iron Deficiency Detection

• MCH decreases earlier than MCV in developing iron deficiency 1, 3
• MCH has slightly better diagnostic accuracy than MCV for detecting iron deficiency in children and young adults 3
• In inflammatory bowel disease, MCH is a useful variable for detecting iron-restricted anemia 1

Limitations and Considerations

1. Diagnostic Accuracy:

   • MCH, MCV, and MCHC have only moderate accuracy in diagnosing empty iron stores (area under ROC curve 0.68-0.96) 3
   • Normal values do not exclude iron deficiency in anemic patients 3

2. Technical Considerations:

   • High triglyceride levels can cause erroneously high hemoglobin measurements, affecting MCH and MCHC calculations 4
   • Sample storage time and patient-specific variables like serum glucose can affect measurements 1

3. Interpretation Challenges:

   • Microcytosis and macrocytosis may coexist, neutralizing each other and resulting in normal MCV despite underlying pathology 1
   • In such cases, an elevated red cell distribution width (RDW) can help identify underlying iron deficiency 1

Clinical Application Algorithm

1. Initial Assessment:

   • Review MCH and MCHC alongside MCV, hemoglobin, and RDW
   • Low MCH with normal MCHC suggests early iron deficiency 1
   • Low MCH and MCHC with low MCV strongly suggests iron deficiency anemia 1

2. Further Evaluation Based on MCH/MCHC Patterns:

   • For low MCH/MCHC: Check serum ferritin, transferrin saturation, and CRP
   • For normal MCH/MCHC with anemia: Consider reticulocyte count to assess bone marrow response 1
   • For unexpectedly high MCHC: Critically evaluate the peripheral smear for hemolytic disorders 2

3. Advanced Assessment:

   • In complex cases, consider additional markers like reticulocyte hemoglobin content (RetHb) for early detection of iron-restricted erythropoiesis 1
   • For chronic disease patients, evaluate both MCH and inflammatory markers to distinguish between iron deficiency anemia and anemia of chronic disease 1

By understanding and correctly interpreting MCH and MCHC values, clinicians can more accurately diagnose various types of anemia and guide appropriate treatment decisions to improve patient outcomes.