A routine complete blood count (CBC) evaluates Mean Corpuscular Volume (MCV) and Mean Corpuscular Hemoglobin (MCH). When these values appear elevated, it signals specific changes in red blood cells that warrant further understanding. This article explains what high MCV and MCH values indicate and outline their common underlying causes.
Deciphering MCV and MCH
Mean Corpuscular Volume (MCV) indicates the average size of red blood cells in a blood sample. A normal MCV typically falls within 80 to 100 femtoliters (fL). When the MCV is above 100 fL, it is considered high, a condition referred to as macrocytosis.
Mean Corpuscular Hemoglobin (MCH) measures the average amount of hemoglobin in each red blood cell. Hemoglobin is the protein in red blood cells that binds to oxygen for transport throughout the body. A normal MCH generally ranges between 27 and 33 picograms (pg) per cell. An MCH value exceeding this range indicates more hemoglobin per cell. High MCH often accompanies high MCV, as larger red blood cells can hold more hemoglobin.
Common Causes of Elevated MCV and MCH
Elevated MCV and MCH levels often indicate macrocytic anemia, where the body produces abnormally large red blood cells. Several factors can contribute to these elevated values.
Vitamin B12 and folate deficiencies are common causes of high MCV and MCH. Both vitamins are essential for DNA synthesis and red blood cell development in the bone marrow. When there is a deficiency, red blood cells cannot divide properly, leading to the production of fewer, but larger and often immature, red blood cells. Vitamin B12 deficiency can impair the maturation of red blood cells, resulting in larger cells that also contain more hemoglobin. Insufficient folate also leads to elevated MCV.
Liver disease and excessive alcohol consumption also frequently lead to elevated MCV and MCH. Liver disorders, such as cirrhosis or hepatitis, can disrupt the intricate processes of blood cell production and processing. In individuals with liver disease, changes in the red blood cell membrane’s lipid composition can affect its surface area, causing an increase in MCV. Chronic alcohol intake can directly damage bone marrow and interfere with folate metabolism, contributing to the production of larger red blood cells. MCV elevation related to alcohol typically appears after several weeks of heavy drinking, defined as consuming 60 grams or more of alcohol daily.
Hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone, can also be associated with elevated MCV. Thyroid hormones play a role in regulating hemoglobin synthesis and overall red blood cell production. Studies have shown that MCV values can increase in both overt and subclinical hypothyroidism. In some cases, hypothyroidism, particularly autoimmune thyroiditis like Hashimoto’s, can lead to impaired absorption of vitamin B12, further contributing to macrocytosis.
Certain medications can interfere with red blood cell production, resulting in elevated MCV. Examples include some chemotherapy drugs, which disrupt DNA metabolism, and certain antiretroviral medications used to treat HIV. Anticonvulsant drugs can also affect red blood cell maturation and production, leading to an increase in MCV.
Myelodysplastic syndromes (MDS) represent a group of disorders where the bone marrow functions abnormally, leading to ineffective production of blood cells. This dysfunction results in defective blood cell formation, causing an increase in both MCH and MCV levels. In MDS, the bone marrow produces poorly formed or non-functional blood cells that often die prematurely, leading to conditions like anemia where the red blood cells are abnormally large.
When to Seek Medical Advice
Receiving blood test results showing high MCV and MCH levels warrants consultation with a healthcare professional. These values are indicators, not a definitive diagnosis, and require further evaluation to determine the underlying cause. Self-diagnosis or delaying professional medical advice is not recommended, as the conditions causing these elevations can range from easily treatable nutritional deficiencies to more complex disorders.
A healthcare provider will review your complete medical history, including any medications you are taking, your dietary habits, and alcohol consumption. They may also perform a physical examination to look for other signs or symptoms. To pinpoint the exact cause of elevated MCV and MCH, additional diagnostic tests may be ordered. These often include specific vitamin B12 and folate level tests, liver function tests, and thyroid studies. A peripheral blood smear, where blood cells are examined under a microscope, can also provide valuable insights into the size and shape of red blood cells and other cell abnormalities.