If your MCV or MCH was abnormal on a recent blood test, you might be curious about what the results could indicate. This page will explain what MCV and MCH measure, why doctors order these tests, what elevated levels may indicate, and factors that could affect the results.

What are MCV and MCH measurements?

MCV (Mean Corpuscular Volume): This measurement refers to the average size of your red blood cells. It's an can be an indicator of your blood's health and can help diagnose different types of anemia and other blood disorders.

MCH (Mean Corpuscular Hemoglobin): MCH measures the average amount of hemoglobin inside your red blood cells. Hemoglobin is the protein that carries oxygen throughout your body.

Why does a doctor order MCV and MCH tests?

Anemia Diagnosis: MCV and MCH measurements are most helpful when a patient has a low Hemoglobin (Hgb) or Hematocrit (Hct). They can help your doctor diagnose the type and severity of anemia. Anemia occurs when your blood doesn't have enough red blood cells or hemoglobin to carry oxygen effectively.

What can an abnormal MCV or MCH level mean?

Elevated MCV:

• Macrocytic Anemia: A high MCV may indicates macrocytic anemia if your hemoglobin is also low, where red blood cells are larger than normal due to deficiencies in vitamin B12 or folate.

Less common

• Liver Disease: Certain liver diseases can cause elevated MCV levels due to impaired production of blood components.
• Alcohol Abuse: Chronic alcohol abuse can lead to macrocytosis, where red blood cells are larger than normal.

Low MCV :

• Iron Deficiency Anemia: The most common cause of low MCV is iron deficiency, where there is a lack of iron available for the production of hemoglobin, resulting in smaller than normal red blood cells (microcytes).
• Thalassemia: The second most common cause of a low MCV is Thalassemia trait. This is a genetic disorder where the body produces abnormal hemoglobin, leading to smaller red blood cells. If the patient has only one copy of this gene from one parent they have the trait which means they are a carrier but don't have the actual disease. Having two copies can cause severe anemia.

NOTE: Patients with Thalassemia trait or Thalassemia anemia will usually have a normal or high RBC level where as patients who have a low MCV due to iron deficiency will usually have a low RBC

Less common

• Chronic Disease: Certain chronic inflammatory conditions, such as chronic kidney disease or rheumatoid arthritis, can lead to low MCV due to decreased red blood cell production.
• Lead Poisoning: Lead toxicity can interfere with hemoglobin production and cause microcytic anemia.
• Bone Marrow Disorders: Conditions affecting the bone marrow, such as myelodysplastic syndromes, can result in decreased red blood cell production and microcytic anemia.
• Certain Medications: Some medications, such as chemotherapy drugs or antiretrovirals, can suppress bone marrow function and lead to low MCV.

Elevated MCH:

• Hyperchromic Anemia: An elevated MCH can indicate hyperchromic anemia, where red blood cells have more hemoglobin than usual. This can be caused by conditions such as hemolytic anemia or vitamin B6 deficiency.
• Thalassemia: Some types of thalassemia can cause elevated MCH levels due to abnormal hemoglobin production.

Low MCH:

• Iron Deficiency Anemia: Similar to low MCV, iron deficiency can also cause hypochromic anemia, where red blood cells have less hemoglobin than normal.
• Thalassemia: Certain types of thalassemia can result in low MCH due to abnormal hemoglobin production.

Less Common

• Lead Poisoning: Lead toxicity can lead to inadequate hemoglobin synthesis and hypochromic anemia.
• Chronic Diseases: Chronic inflammatory conditions or chronic infections can affect hemoglobin synthesis and result in hypochromic anemia.
• Sideroblastic Anemia: This rare genetic or acquired disorder affects iron utilization for hemoglobin synthesis, leading to hypochromic red blood cells.
• Vitamin B6 Deficiency: Inadequate intake or absorption of vitamin B6 can impair hemoglobin production and cause hypochromic anemia.
• Other Considerations:
• Pregnancy: Mild decreases in MCV and MCH can sometimes occur during pregnancy due to dilutional effects of increased blood volume.
• Malnutrition: Severe malnutrition, especially protein-calorie malnutrition, can lead to decreased red blood cell production and microcytic, hypochromic anemia.
• Chronic Illnesses: Long-term illnesses that affect overall nutritional status or bone marrow function can contribute to low MCV or MCH.

What can cause false positive elevations in MCV or MCH levels?
Certain factors can temporarily affect MCV and MCH levels without indicating an underlying health issue:

• Medications: Certain medications, such as chemotherapy drugs or antiretrovirals, can affect red blood cell size and hemoglobin content.
• Nutritional Supplements: Taking high doses of vitamin B12 or folate supplements can temporarily alter MCV levels.
• Pregnancy: Pregnancy can cause physiological changes in blood volume and red blood cell size, affecting MCV and MCH levels.
• Recent Blood Loss or Transfusion: Recent blood loss or transfusion can temporarily affect red blood cell size and hemoglobin content.

Conclusion
Understanding MCV and MCH measurements in your blood test results can provide valuable insights into your overall health, especially regarding red blood cell function and the presence of anemia or other blood disorders. If your MCV or MCH levels are elevated, it's important to follow up with your healthcare provider to determine the underlying cause and discuss appropriate next steps.

By discussing your test results with your doctor, you can gain a clearer understanding of your health status and any necessary treatments or lifestyle adjustments. Remember that while abnormal MCV and MCH levels can be concerning, in most cases if the abnormalities are mild and  Hgb and Hct are normal they most likely are of no consequence.