Mean platelet volume (MPV) is part of a simple blood test that measures average platelet size. MPV may give doctors another clue when they’re looking for the cause of a low platelet count. However, MPV alone can’t diagnose immune thrombocytopenia (ITP) or rule out other causes of a low platelet count.

This article explains what MPV is, how it relates to ITP, and how doctors interpret MPV results along with other health information.

What Is an MPV Test?

Platelets (thrombocytes) are small pieces of cells that help form blood clots. They’re made in the bone marrow — spongy tissue found inside your bones.

The number, shape, and size of your platelets can provide information about your blood and platelet health. Doctors may use several blood tests to evaluate a low platelet count or bleeding disorder.

Your MPV test shows the average size of your platelets. MPV is part of a complete blood count (CBC) test, which gives information about your:

• Red blood cells
• White blood cells
• Platelets

🗳️ Have you had mean platelet volume (MPV) measured as part of your immune thrombocytopenia (ITP) bloodwork?

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MPV Results

MPV blood test results can’t confirm a specific diagnosis. Doctors interpret MPV along with your platelet count, other test results, symptoms, and health history.

There is no single normal MPV range that applies to everyone. Results can vary based on the laboratory, testing machine, and how the blood sample was handled. Use the reference range shown on your own lab report.

What High and Low MPV Results May Mean

A high MPV means that the platelets are larger than the laboratory’s usual range. A low MPV means that they’re smaller. These results may give doctors clues about what’s happening with your platelets, but they don’t show the cause by themselves.

Many health conditions and testing factors can affect MPV, so doctors interpret it along with the platelet count, symptoms, medical history, and other tests. Health conditions that have been linked to a high MPV include:

• ITP
• Diabetes
• Heart disease
• Hyperthyroidism
• Myeloproliferative diseases (blood disorders that affect the bone marrow)

A low MPV means the platelets are smaller than the laboratory’s usual range. Low results have been reported in several health conditions, but MPV can’t show why the platelets are small or whether the bone marrow has slowed platelet production. Doctors must interpret the result with the platelet count and other findings.

Why Does Platelet Size Matter in ITP?

In ITP, the immune system mistakenly attacks platelets. ITP can also make it harder for the body to produce enough new platelets. Some people with ITP have larger platelets and a higher MPV, but not everyone does.

MPV is often reported automatically as part of a CBC. It may provide useful information, but it can’t confirm ITP.

Diagnosing ITP involves ruling out other causes of low platelet counts. It’s important to get the correct diagnosis because different causes of thrombocytopenia require different treatment. Doctors usually look at several factors, including underlying health conditions and medications.

To look for the cause of a low platelet count, your doctor may ask about your symptoms, health history, family history, and medicines. A peripheral blood smear lets a healthcare professional examine your blood cells under a microscope. These findings can help identify or rule out other causes of thrombocytopenia.

MPV May Be Higher in ITP Than in Some Other Types of Thrombocytopenia

Some studies have looked at whether MPV can help doctors distinguish ITP from other causes of thrombocytopenia. People with ITP may have larger platelets than people whose low platelet counts are caused by reduced platelet production. However, platelet sizes overlap between these groups, so MPV can’t reliably tell the conditions apart in one person.

A high MPV in ITP may be a sign of rapid platelet turnover. This means that as platelets are destroyed, the bone marrow may respond by making and releasing more platelets. Newly released platelets tend to be larger than older ones.

One meta-analysis looked at 13 studies that included 597 people with ITP and 866 with thrombocytopenia caused by reduced platelet production. The average MPV was 11.17 femtoliters (units of volume) in people with ITP, compared with 9.14 femtoliters in those with reduced platelet production.

These averages don’t provide a clear cutoff for diagnosing ITP in one person. MPV results can overlap between ITP and other causes of thrombocytopenia, and results can differ depending on the testing machine and how the blood sample was handled. Doctors use MPV as just one clue among many when evaluating a low platelet count.

How Does MPV Vary in Other Platelet Disorders?

On the surface, ITP can look like many other causes of low platelets. MPV testing may give doctors another clue when distinguishing ITP from thrombocytopenia caused by reduced platelet production.

MPV in Wiskott-Aldrich Syndrome

Wiskott-Aldrich syndrome (WAS) is a genetic condition that causes a decreased platelet count. WAS typically causes microthrombocytopenia (fewer, smaller platelets than normal).

People with WAS often have a low MPV because their platelets are smaller. The WAS gene gives the body instructions for making the WASP protein, which helps blood and immune cells work normally. Depending on the gene change, a person may make little or no working WASP protein.

As a result, people with Wiskott-Aldrich syndrome usually have a low platelet count. Their platelets are often smaller than normal, although platelet size can vary.

Both ITP and WAS can cause potentially dangerous bruising and bleeding. MPV may give doctors a clue about the cause of thrombocytopenia, but it can’t reliably tell these disorders apart on its own. Doctors also consider symptoms, health and family history, a blood smear, and other tests.

MPV in Aplastic Anemia

Aplastic anemia occurs when the bone marrow doesn’t produce enough red blood cells, white blood cells, and platelets. Aplastic anemia can develop after certain viral infections, and many cases involve the immune system attacking bone marrow stem cells.

Certain inherited conditions also cause bone marrow failure. When the bone marrow can’t make enough new cells, it causes symptoms like:

• Low red blood cell levels — Fatigue and shortness of breath
• Low white blood cell levels — Higher risk of infections
• Low platelet levels — Easy bruising and bleeding

MPV results can vary in people with aplastic anemia. A low MPV may occur, but MPV alone can’t show whether the bone marrow is producing enough new platelets. Doctors rely on blood counts and, when needed, bone marrow tests to diagnose aplastic anemia and distinguish it from ITP.

What Factors Affect Mean Platelet Volume?

MPV test results can vary depending on how the sample is collected and handled, the analyzer used, your overall health, and other factors.

Platelets clump together to help form blood clots. A chemical commonly used to process blood samples can sometimes trigger platelet clumping. These clumps can make the platelet count appear lower than it really is.

Platelet clumps can also confuse an automated blood-counting machine. The MPV may be inaccurate, flagged, or not reported. A peripheral blood smear can show whether clumping occurred, and in some cases, another blood sample may be collected in a different type of tube.

Some studies have reported links between MPV and the factors below. However, findings aren’t always consistent, and these factors should not be used to explain an individual result without a doctor’s guidance:

• Age and sex
• Diet, alcohol use, and smoking
• Pregnancy, birth control use, and menstruation (having your period)
• Physical activity

Changes in MPV may also happen with ITP treatment, but the evidence is limited. One small study that included 70 people with newly diagnosed ITP found that those who responded to treatment had a lower MPV after treatment.

About half of these participants received intravenous immunoglobulin (IVIG) with steroids. Among people who responded to treatment, average MPV dropped from 11.09 femtoliters to 9.32 femtoliters. This was only one study, so more research is needed to learn whether MPV consistently changes with ITP treatment.

Because the evidence is limited, doctors don’t normally use MPV changes alone to decide whether an ITP treatment is working.

Ask Your Doctor About an MPV Test for ITP

MPV is often included in standard bloodwork and may provide another clue about your platelets. However, it can’t diagnose ITP, rule out other conditions, or show on its own whether treatment is working.

Doctors mainly monitor ITP by checking platelet counts, bleeding symptoms, treatment response, and treatment side effects. Your doctor can explain how your MPV fits with your other test results and overall health.