Mean Corpuscular Hemoglobin (MCH)
MCH is a measure of the average amount of hemoglobin contained in each red blood cell, expressed in picograms (pg), and serves as an important diagnostic parameter for various types of anemia, particularly iron deficiency anemia. 1
Definition and Measurement
MCH is calculated as part of a complete blood count (CBC) by automated cell counters using the formula:
MCH = (Hemoglobin × 10) ÷ Red Blood Cell count
Normal MCH values typically range between 27-31 pg in adults.
Clinical Significance
Iron Deficiency Detection
MCH is particularly valuable in diagnosing iron deficiency anemia for several reasons:
- It decreases in iron deficiency, resulting in hypochromic red cells
- It is more reliable than MCV (Mean Corpuscular Volume) as a marker of iron deficiency as it is:
- Less dependent on storage conditions
- Less affected by the specific counting machine used
- More sensitive for detecting iron deficiency than MCV 1
- It shows reduction in both absolute and functional iron deficiency (FID)
Diagnostic Value
Recent research indicates MCH has good diagnostic accuracy for iron deficiency:
- The area under the ROC curve for MCH in diagnosing iron deficiency is 0.67, making it a fairly accurate diagnostic parameter 2
- When combined with other red cell indices, MCH contributes significantly to iron deficiency diagnosis without requiring additional expensive testing
Interpretation in Different Conditions
Low MCH (Hypochromia)
Low MCH values may indicate:
- Iron deficiency anemia (primary cause)
- Thalassemia (particularly when MCV is reduced disproportionately to anemia level)
- Sideroblastic anemia
- Anemia of chronic disease 1
Normal or High MCH
Normal or elevated MCH may be seen in:
- Macrocytic anemias (vitamin B12 or folate deficiency)
- Liver disease
- Alcoholism
- Reticulocytosis
Limitations and Considerations
MCH has several limitations that should be considered when interpreting results:
- Its specificity for iron deficiency is limited as hypochromia also occurs in other conditions
- MCH values may be unreliable in newborns for diagnosing certain conditions like alpha-thalassemia 3
- MCH should be interpreted alongside other parameters such as ferritin, transferrin saturation, and red cell distribution width (RDW) for accurate diagnosis 4
- In inflammatory states, MCH should be interpreted with caution as inflammation can affect red cell parameters
Clinical Application
When evaluating anemia, MCH should be assessed as part of a comprehensive panel including:
- Complete blood count with hemoglobin measurement
- Iron studies (serum ferritin and transferrin saturation)
- Red cell morphology assessment 4
If low MCH is detected with normal iron studies, especially in patients with appropriate ethnic background, hemoglobin electrophoresis should be considered to rule out hemoglobinopathies like thalassemia 1.
Monitoring Treatment
MCH is useful for monitoring response to iron therapy, with values expected to normalize as hemoglobin content in red cells increases following successful treatment of iron deficiency anemia.
MCH provides valuable diagnostic information about red blood cell hemoglobin content and serves as an important parameter in the evaluation and management of various types of anemia, particularly iron deficiency anemia.