MCV blood test is a very common test which is part of the test called Complete Blood count (CBC). CBC is also known with the names of Complete blood picture (CBP), Full blood count (FBC), Full blood picture (FBP). Whenever we go to a doctor, we come across this test very commonly as part of the blood investigations. But, many of us don’t know the significance of all the components of the CBC test including the MCV blood test. Let us try to learn more about MCV blood test in this article.
What does MCV blood test mean?
MCV is the abbreviation of Mean corpuscular volume. MCV blood test is the measurement of the volume of Red Blood Cells or RBC’s or erythrocytes or red blood corpuscles in the specimen of blood. It reflects the volume of RBC’s in our body. With the help of this MCV blood test, we can know the average size of all the red blood cells in our body.
We need to know the normal values of MCV blood test at first. Based on this, if the MCV is high, it means that the RBC’s are larger in size. If the MCV is low, it means the Red blood cells are smaller in size in comparison to the normal RBC’s.
We all know that anemia is a very common condition. Many of us might have suffered from anemia or low hemoglobin levels in our blood at some point in our life. But, many of us don’t know that there are many different types of anemia. Doctor’s try to distinguish the types of anemia based on CBC test values.
MCV blood test is an important component of the CBC blood test which helps to differentiate amongst the types of anemia. MCV is mainly used along with other parameters in the CBC test like MCH (Mean corpuscular hemoglobin), MCHC (Mean corpuscular hemoglobin concentration), Hemoglobin levels, etc to determine the type of anemia.
MCV blood test calculation:
In most of the laboratories, MCV is reported automatically by the machines in the CBC report. But, we can also calculate the CBC manually. There are two parameters from the CBC which are used as part of the formulas to calculate MCV. They are the Packed cell volume or PCV or Hematocrit, and the Red blood cell count. MCV is reported in fL, which is the abbreviation for femtoliters. The formulas for MCV calculation are:
MCV = Hematocrit (in L/L)/RBC count (in millions/ml)
MCV = Hematocrit (in L/L)/RBC count (in 10¹²/L) × 1000
MCV= Hematocrit (%) × 10 / RBC count [in 10¹²/L]
MCV Normal range:
There might be variation in the value of MCV based on the laboratory and the age group of the patient. Let us look at some of the reference ranges for MCV blood test in people of different age groups.
- The normal reference range for MCV blood test in newborns: 95 to 121 fL
- The normal reference range for MCV blood test in 6 months to 2 years kids: 70 to 86 fL
- The normal reference range for MCV blood test in girls aged 12 to 18 years: 78 to 102 fL
- The normal reference range for MCV blood test in boys aged 12 to 18 years: 78 to 98 fL
- The normal reference range for MCV blood test in adults: 80 to 96 fL/Red cell.
If MCV is less than 80 fL in adults, then Red blood cells are smaller or microcytic than normal blood cells. If MCV is more than 96 fL in adults, then the red blood cells are larger in size or macrocytic in comparison to the normal red blood cells.
Reasons for performing MCV blood test:
- As an integral part of CBC blood test, used for regular screening
- Pallor or pale appearance of the patient (skin being pale or conjunctiva being pale)
- Fatigue or getting tired easily
- Spleen becoming enlarged
- After severe blood loss after an injury
- To monitor patients condition in disorders like Burns, COPD, liver, and kidney disorders
- To review effects of medications or drugs on red blood cells
Collection of the specimen for MCV blood test:
- Blood specimen is collected for performing MCV blood test
- No special preparation is required by the patient prior to the test
- A band is tied 2 to 3 inches above the elbow in the arm, to facilitate the easy removal of blood
- Then the area over the elbow is cleaned with alcohol swab or spirit
- Then a syringe with needle is inserted slowly into the superficial vein over the elbow pit
- Then blood is slowly withdrawn into the syringe
- Then the needle along with syringe is withdrawn slowly and a band-aid is placed over the blood collection site
- The blood is collected into an EDTA tube, which has EDTA as additive for anticoagulation
Types of anemia based on MCV values:
Based on the MCV and MCHC values, anemia is divided into three main types. They are:
- Normocytic-Normochromic anemia: MCV and MCHC values are normal in it, but hemoglobin levels are low
- Microcytic hypochromic anemia: MCV, MCHC, and hemoglobin levels are low in it
- Macrocytic anemia: MCV is high, but hemoglobin levels are low
Causes of low MCV in MCV blood test:
Iron deficiency anemia:
Iron deficiency anemia is the most common type of anemia in the world. Majority of us are anemic, and when the doctor says to take iron syrups or tablets, it is to correct the iron deficiency anemia. It is also the most common type of microcytic hypochromic anemia.
Our Red blood cells contain hemoglobin, and the RBC’s are red in color due to hemoglobin content in them. The hemoglobin in the RBC’s is responsible for carrying the oxygen and then supplying to cells and organs throughout the body.
Hemoglobin is made of 2 parts. They are the globin and haem. Globin part is made of protein, and it has 2 subunits alpha and beta globin. Another part of the hemoglobin, that is haem is made of iron. If there is a deficiency of iron in the body, the haem content reduces, which leads to a reduction of hemoglobin levels and also the size of RBC’s. This makes MCV smaller.
There are many reasons for the development of iron deficiency anemia like:
- Decreased intake of iron-containing foods like green leafy vegetables, dates, etc
- Decreased absorption of iron from the body due to intestinal or gastric problems
- Decreased absorption of iron due to vitamin C deficiency, as vitamin C is necessary for the absorption of iron
- Loss of blood due to injury, etc leading to loss of iron
- Infestation of worms like hookworm, which is more common amongst kids in poverty-stricken families
- Increased demand for iron and hemoglobin, for example during pregnancy, breastfeeding, etc
- Increased blood loss due to conditions like menorrhagia or excessive bleeding during menses in women
In this condition, iron is not properly inserted into the haem part of the hemoglobin. Due to this, it leads to low MCV and smaller sized RBC’s. There are many reasons for the development of sideroblastic anemia like:
- Lead poisoning (by eating lead-containing fish, paints on the wall, etc)
- Copper deficiency
- Myelodysplastic syndrome
- Side effects of anti-TB drugs
- As a hereditary defect in certain cell structures
Thalassemia is a hereditary or genetically acquired disease. In this disease, there is a defect in the production of alpha, and beta globin chains of the hemoglobin. In alpha thalassemia, there are very less or absent alpha chains of globin. In Thalassemia major, a subtype of beta thalassemia, there are very less or absent beta globin chains of hemoglobin.
There are also other subtypes of beta thalassemia like Thalassemia intermedia, and Thalassemia minor, based on the number of beta globin chains in the hemoglobin present. As the globin chain production is defective, there is low MCV in Thalassemia patients.
Anemia of chronic disease:
There are many diseases, and inflammatory conditions in which there are low MCV values, and this is called anemia of chronic disease. There are many reasons for developing anemia of chronic disease like reduced iron availability, reduction in the lifespan of the RBC’s, decreased the production of erythropoietin which is necessary for the production of RBC’s, etc. The diseases in which anemia of chronic disease can occur are:
- Systemic lupus erythematosus or SLE
- Infective endocarditis
- Crohn’s disease
- Sarcoidosis, etc
Causes of high MCV in MCV blood test:
If the MCV is high in an MCV blood test, it means the red blood cells are large or macrocytic. It is most commonly caused by a deficiency of vitamins like B12 or Folate. The deficiency of these vitamins causes a defect in the DNA of the RBC’s. This leads the red blood cells to retain a large amount of cytoplasm in their cell. This leads to high MCV values in MCV blood test or the RBC’s to be macrocytic.
Vitamin B12 deficiency:
Vitamin B12 deficiency is one of the major causes of macrocytic anemia. It can occur in vegan or vegetarian people more commonly, as the B12 vitamin is abundant in animal-based foods and scarce in the plant-based foods. This deficiency can also occur if a person is alcoholic or consumes alcohol more frequently. Deficiency of an enzyme called transcobalamin can also lead to a defect in the metabolism of vitamin B12 and to its deficiency.
Several drugs used to treat various disorders can have antifolate effects. Due to this, it can lead to folate deficiency and then to macrocytic anemia with high MCV values.
Excess alcohol intake can damage the DNA of the red blood cells leads to the formation of the macrocytic cells.
Other causes of Macrocytic anemia:
- Myelodysplastic syndrome
- Liver disorders like cirrhosis
- Aplastic anemia
- Disease-modifying antirheumatic drugs or DMARDs like Methotrexate
- Side effects of other cytotoxic drugs like Cyclophosphamide, etc
By now, you must have understood all the different aspects of MCV blood test, like the normal range, how it is performed, how MCV is calculated, causes for high MCV levels and low MCV levels.
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