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Dr. Shreya Gupta
BDS, MDS - Oral and Maxillofacial Pathology
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Dr. Ashish Ranjan
MBBS, MD (Pharmacology)
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Understanding PDW

What is PDW?

A PDW or Platelet Distribution Width test measures the variation in platelet size, also called platelet anisocytosis, and is calculated from the distribution of individual platelet volumes. PDW reflects how uniform the platelets are in size and is often done as a part of a complete blood count (CBC) test.

Platelets, also known as thrombocytes, are small blood cells that help the blood to clot if there is an injury and prevent excessive bleeding. If one of your blood vessels gets damaged, it sends a signal to platelets. Platelets then arrive at the injury site and form a plug (clot) to repair the damage. This is called platelet activation.

PDW is a simple platelet index, which increases during platelet activation. PDW is a more specific marker of platelet activation since it does not increase during simple platelet swelling. A PDW, which is usually done along with some additional tests as a part of CBC, can help your doctor investigate multiple conditions, including thrombocytopenia (low platelet count) and thrombocytosis (high platelet count). Your doctor may suggest a PDW test if you experience excessive bleeding or bruising or if you have conditions that can affect your platelet count, such as iron deficiency anemia.

Fasting is unnecessary before getting a PDW, and you may eat or drink as per your daily routine. However, you should inform your doctor if you are taking any medicines as they may affect your test results.

Test result ranges are approximate and may differ slightly between different labs depending on the methodology and laboratory guidelines. Talk to your doctor about your specific test results. The results will help them determine your medical condition and formulate an overall treatment plan.

What does PDW measure?

A PDW test reflects variability in platelet size, and is considered a marker of platelet function and activation (clot formation in case of an injury). This marker can give you additional information about your platelets and the cause of a high or low platelet count. Larger platelets are usually younger platelets that have been recently released from the bone marrow, while smaller platelets may be older and have been in circulation for a few days. Higher PDW values reflect a larger range of platelet size, which may result from increased activation, destruction and consumption of platelets.


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