Platelet Distribution Width (PDW): A Guide

What is PDW?

Platelet distribution width (PDW) is a complete blood count (CBC) parameter measured in femtoliters (fL) or percentages. It shows how much platelets differ from each other in size. The higher the PDW, the greater the variability in platelet size -- both very small and very large platelets are present in the blood.

PDW complements other platelet parameters -- platelet count, MPV, and plateletcrit -- helping the doctor more precisely assess platelet production and destruction processes in the bone marrow.

Reference Range

The typical PDW value for adults is 9.0-17.0 fL. In some laboratories, PDW is reported as a percentage, so it is always important to compare your result with the specific reference ranges provided by the laboratory.

A small deviation from the reference range does not necessarily indicate disease -- the doctor always evaluates PDW in the context of other parameters.

Why might PDW be elevated?

An elevated PDW indicates greater variability in platelet size, which may signify:

• Active platelet production -- the bone marrow is intensively producing new (larger) platelets due to increased demand
• Myeloproliferative disorders -- certain bone marrow diseases cause uneven platelet production
• Sepsis or severe infection -- PDW elevation can be an early sign of sepsis
• Thromboembolic conditions -- high PDW is associated with increased thrombosis risk
• Malignant tumors -- certain cancer types can alter platelet production
• Iron deficiency

Why might PDW be decreased?

A decreased PDW means that platelets are similar in size (low variability). This may be:

• A normal finding -- if all other parameters are within range, a low PDW usually raises no concern
• Bone marrow suppression -- when platelet production is reduced, new platelets may be uniform in size
• Aplastic anemia
• Effects of certain medications (e.g., chemotherapy)

It is important to know that a decreased PDW is rarely evaluated in isolation -- it is always analyzed together with other CBC parameters.

What to do next?

If the PDW result is outside the reference range:

1. Do not panic -- PDW alone rarely indicates a serious disease 2. Pay attention to other platelet parameters -- platelet count, MPV, plateletcrit 3. Discuss the result with your doctor, especially if you have symptoms of inflammation, infection, or bleeding 4. Repeat the test if the doctor recommends -- this will help assess the trend over time 5. Maintain a healthy lifestyle -- a balanced diet with adequate iron, folic acid, and B12 supports normal platelet production

Monitoring over time

PDW is not a parameter that typically needs to be monitored separately. It is evaluated as part of the CBC when the doctor monitors platelet changes. Regular CBCs help detect whether platelet size variability is changing -- this can reflect developing or resolving inflammation, bone marrow response to treatment, or disease dynamics.

If PDW was elevated due to infection, its normalization indicates the body is recovering.

Questions for your doctor

• Is my PDW change clinically significant given the other parameters?
• Do I need additional tests because of the elevated PDW?
• Could the abnormal PDW be related to my current condition or medications?
• How often should I repeat the complete blood count?
• Are there warning signs that should prompt me to seek urgent care?