A low mean corpuscular volume (MCV) indicates that the size of a person's red blood cells is below average, and a low mean corpuscular hemoglobin (MCH) measurement indicates a person's blood has low hemoglobin levels.
If a blood test has low numbers of MCV and MCH, it can signal that a person has anemia. Depending on whether one or both numbers are low, doctors can determine what type of anemia the patient has. A low MCV count means that the patient may have microcytic anemia. A low MCH level is due to hypochromic anemia.
The Role of Hemoglobin
Hemoglobin contains iron, which is necessary for bringing oxygen to cells throughout the body. It is also the most plentiful protein in red blood cells. Hemoglobin levels vary widely, and an abnormally high or low level might not be clinically significant. However, there are ideal standards for a hemoglobin count based on age and gender. For adult males, the ideal range falls between 13.5 and 17.5 grams per deciliter. That number is 12.0 to 15.5 grams per deciliter for adult women. Doctors usually make the diagnosis of anemia when numbers fall below this range. Although anemia can explain a low MCV or MCH level, doctors must determine the underlying cause of anemia. A folic acid deficiency is the most common cause. However, some types of kidney disease, liver disease, hypothyroidism and bone marrow cancers can cause anemia. Some individuals have a genetic condition called thalassemia, which causes low levels of red blood cells and hemoglobin.
Complete Red Blood Cell Count
MCV and MCH are components of a complete red blood cell (RBC) count. The purpose of the RBC is to determine how much oxygen the red blood cells are carrying as they move around the body. Doctors may discover that a person has low MCV or low MCH levels through a routine blood test. They also use this test to determine if erythropoiesis, the production of red blood cells, is normal. The normal range of red blood cells varies by gender and age. Other factors that influence the number of red blood cells in a person's body are altitude, exercise, diet, kidney function and the use of drugs or alcohol.
Although a low level of MCV or MCH might not produce symptoms, doctors might order the test if patients complain of symptoms associated with anemia, reduced immune function and low levels of oxygen in the blood. Easy bleeding or bruising and frequent infections may signal that a patient has a problem with his or her red blood cells. General symptoms of anemia include shortness of breath, dizziness, headaches, leg cramps and fatigue. Low energy levels and insomnia have also been reported in anemic patients. Anemia attributed to specific causes can have its own set of symptoms. Anemia from iron deficiency, for example, can cause a hunger craving for unusual substances like paper and dirt. People with this type of anemia might also develop cracks at the edges of their mouths. Anemia stemming from a Vitamin B12 deficiency can cause tingling, numbness and a decreased sensation of touch.
When a blood test comes back showing low MCV or MCH levels, doctors may order additional tests to determine the underlying cause.