Difference Between MCH and MCHC in Blood Tests
MCH (Mean Corpuscular Hemoglobin) measures the average amount of hemoglobin per red blood cell, while MCHC (Mean Corpuscular Hemoglobin Concentration) measures the average concentration of hemoglobin within a given volume of packed red blood cells. 1
Key Differences
MCH (Mean Corpuscular Hemoglobin)
- Measures the absolute weight of hemoglobin in an average red blood cell
- Reported in picograms (pg) per cell
- Calculation: Total hemoglobin ÷ Red blood cell count
- Not affected by cell volume
- May be more reliable marker of iron deficiency than MCV as it is less dependent on storage and counting machine used 1
MCHC (Mean Corpuscular Hemoglobin Concentration)
- Measures the concentration of hemoglobin relative to the size of the cell
- Reported in grams per deciliter (g/dL)
- Calculation: MCH ÷ MCV (or Hemoglobin ÷ Hematocrit)
- Affected by cell volume changes
- Has physiological upper limits due to hemoglobin solubility constraints 2
Clinical Significance
MCH
- Low MCH (hypochromia) indicates:
- Iron deficiency anemia
- Thalassemia
- Anemia of chronic disease
- MCH is reduced in both absolute and functional iron deficiency 1
- May be more sensitive for detecting iron deficiency than MCV 1
MCHC
- Low MCHC typically accompanies microcytosis and suggests:
- Inadequate iron availability for hemoglobin synthesis
- Functional iron deficiency despite adequate stores 3
- Abnormally high MCHC (>36 g/dL) is physiologically impossible due to hemoglobin solubility limitations and usually indicates laboratory error or interference 2, 4
Diagnostic Value
Both parameters are part of the complete blood count (CBC) and are used together with MCV (Mean Corpuscular Volume) to classify anemias:
- In iron deficiency anemia: Both MCH and MCHC are typically low 1, 5
- In megaloblastic anemia (B12/folate deficiency): Both may be normal or high
- In thalassemia: MCH is disproportionately low compared to MCV 1
- In anemia of chronic disease: Both may be normal or low 1
Limitations
- Neither MCH nor MCHC alone is highly specific for diagnosing iron deficiency, with diagnostic accuracy (area under ROC curve) of 0.73-0.96 for MCH and 0.68-0.87 for MCHC 5
- Both values can be affected by sample storage conditions, though MCHC is calculated from MCH and MCV, so it inherits the limitations of both measurements 6
- False elevation of MCHC can occur due to cold agglutination, lipid interference, or other laboratory artifacts 4
Practical Application
When interpreting blood tests:
- Look at MCH and MCHC together with other red cell indices (MCV, RDW)
- Low MCH with normal MCHC may indicate early iron deficiency
- Low values of both typically indicate more established iron deficiency
- Normal values do not completely exclude iron deficiency, especially in early stages 5
Hemoglobin is generally preferred over hematocrit for monitoring anemia as it is more stable and less affected by sample storage conditions and hyperglycemia 1, which indirectly affects the reliability of calculated MCHC values.