Mean Platelet Volume (MPV) on Your Lab Results

You may have seen the letters "MPV" as part of your Complete Blood Count (CBC) test, a test which is used in health screening tests, as well as for monitoring treatment for many health conditions. The CBC test assesses your red blood cells (cells that carry oxygen), white blood cells (infection-fighting cells), and platelets (clot-forming cells). MPV (which stands for mean platelet volume) is a measure of the average size of platelets (thrombocytes), a component of your blood which helps your blood clot.

On your CBC you will have a report of your total platelet count as well as "platelet indices" such as MPV. You will notice that there are also indices for your red blood cell count and white blood cell count. These indices give a more accurate description of any problems with your blood cells. In fact, at times a person may have normal levels of blood cells, but an abnormal reading on indices may alert your doctor to a problem. MPV is most helpful in determining the cause of thrombocytopenia, a low platelet count, but can be a helpful test even if your platelet count is normal.

Why is the average size of platelets important, and what does it mean if your MPV is higher or lower than the normal range? Let's talk about the possible causes of a high or low MPV, as well as how MPV may be used to predict risk in people with some medical conditions.

Platelets are the cells responsible for forming clots. They are essential for keeping us from bleeding excessively when we are cut and control bleeding inside of our bodies as well. When a laceration occurs on our skin or inside our bodies, platelets aggregate to plug the hole. Other clotting factors (such as those which are absent in hemophilia) are then called to the scene to prevent further bleeding.

Platelets are produced in the bone marrow by cells called megakaryocytes. The platelets themselves are just pieces of megakaryocytes, without nuclei, released into the bloodstream from the marrow. Usually, younger platelets are larger than older platelets.

In looking at MPV, it's important to look at both the absolute number of platelets and the MPV.

The normal range for platelets (this can vary some between labs) is 150,000 to 450,000 per milliliter. Ordinarily, people can tolerate platelet levels down to 50,000 with only minimal bruising. A platelet level below 20,000, however, can be life-threatening. Platelet indices include:

• MPV (discussed here).
• PDW (platelet distribution width). PDW describes the variation in size of platelets.

In determining the possible cause of an abnormal MPV, it's important to look at whether the platelet count is normal, high, or low.

The first step when a doctor sees that you have an abnormal MPV will be to assess the accuracy of the test. If it looks like there may have been an error with your blood draw, the test will be repeated.

The CBC test requires anticoagulated blood (blood that is drawn into a tube which contains an anticoagulant so the blood won't clot) and is usually drawn into a purple top tube. If blood is drawn into a tube without an anticoagulant, it will clot, giving an abnormal result for both the platelet count and MPV. If your doctor believes clumping may have occurred, another sample will be drawn. Some people need their blood drawn into a different tube altogether, as their platelets may still clump with the anticoagulant used in a purple top tube.

When the MPV value is high, the lab will usually check it with a differential blood smear, a test which looks at the numbers of different types of white blood cells present. The technologist will make and stain a slide of your blood and look at it under the microscope to see if the platelets are clumping together or if you actually have giant platelets. That being said, some people truly have large or giant platelets due to the causes below.

A high MPV is usually a sign that there are more young platelets circulating in your bloodstream. If you have had a procedure such as major surgery, your body is using up platelets to repair the cuts to the blood vessels. In response, your bone marrow releases more of the young, larger platelets, and your MPV rises.

Evaluating a high MPV is most helpful in determining the cause of a low platelet count, and the most common cause is "destruction," or the platelets being destroyed in some way, such as by antibodies you produce (see ITP below).

A high MPV with a high platelet count, in contrast, is often due to primary or essential thrombocytosis (a condition in which the body produces too many platelets, often due to a genetic mutation), or cancer.

A high MPV with a normal platelet count suggests conditions such as hyperthyroidism, or chronic myelogenous leukemia.

Conditions that may cause an elevated MPV include :

• Idiopathic thrombocytopenic purpura (ITP): ITP is a condition in which the immune system destroys platelets. The condition idiopathic thrombocytopenic purpura has a long name, but looking at each of the terms in ITP makes this easier to understand. Idiopathic is a term used to describe a condition of unknown cause. It is doctor lingo for "we don't have a clue" why it occurs. The root word "thrombo" refers to clot (the function of platelets) and "penia" refers to deficiency, so thrombocytopenia refers to a deficiency of platelets. Purpura is the medical term for a bruise, usually a fairly large bruise. (The term petechiae refers to small red marks on the skin (small bruises) which don't blanch when you press on them.) 
• Blood cancers such as leukemia.
• Non-alcoholic liver disease.
• Genetic abnormalities in platelets.
• Bernard-Soulier Disease (giant platelet syndrome).
• Bone marrow stimulating drugs, such as erythropoietin or thrombopoietin.
• Diabetes mellitus.
• Respiratory Diseases.
• Sepsis.
• Hyperthyroidism.

Possible causes of a low MPV can also vary depending on the platelet count. A low MPV with a low platelet count can point towards disorders affecting the bone marrow that slow down or decrease the production of platelets, such as a condition called aplastic anemia. A low MPV with a high platelet count often signifies an infection, inflammation, or cancer. A low MPV with a normal platelet count is common with chronic kidney failure.

Possible causes of a low MPV include:

• Bone marrow failure (older platelets are smaller, so the MPV is low if the bone marrow isn't producing as many).
• Splenomegaly (an enlargement of the spleen). With hypersplenism, platelets are often "sequestered" in the spleen.
• Chronic kidney failure
• Medications that suppress platelet formation (such as chemotherapy drugs).
• Hypothyroidism.
• Iron deficiency anemia.
• HIV/AIDS.

The diagnosis of a high or low MPV will depend on many factors including the platelet count, red blood cell count, and white blood cell count. A bone marrow test may be needed if there is concern about the bone marrow not functioning or that cancer could be present. That said, the evaluation could be as simple as checking thyroid function tests.

In recent years it's been found the MPV may assist in the early diagnosis of heart attacks. The research is young, but it's thought that a higher MPV might both predict the risk that someone with heart disease will have a heart attack, and predict a poorer prognosis in those who have had a myocardial infarction. Likewise, an elevated MPV may be predictive of stroke, as well as provide a clue for those who may do poorly after a stroke. Studies are also looking to see if an elevated MPV may have any role in predicting the risk of blood clots (deep vein thrombosis and pulmonary emboli), as well as peripheral arterial disease.

In addition to a possible role in predicting outcomes with heart disease and stroke, studies have found that MPV may have a predictive role in conditions such as the severity of sepsis in newborns, the prognosis with breast cancer, for distinguishing ovarian cancer from benign ovarian tumors, and even in diagnosing acute appendicitis.

Mean platelet volume (MPV) is a measure of the size of platelets and can play an important role in diagnosing disease whether the platelet count is high, low, or normal. In addition to being a diagnostic test, we are learning that MPV may also be able to play a predictive role in conditions such as heart disease, and if so, could direct physicians as to which people need to be followed more closely or receive more aggressive treatment.