PDW (Platelet Distribution Width) levels, explained
PDW tells you how much your platelets vary in size — a routine part of the full blood count that hints at how actively the bone marrow is making new platelets.
What’s a normal PDW level?
Typical adult reference range, shown for orientation. Your report’s range may differ by lab, age, and sex — the analyzer uses your report’s own ranges when available.
What high and low PDW mean
A value outside the reference range is a flag, not a diagnosis. Here’s what each direction usually points to — and the most common causes.
A high PDW means platelets vary widely in size — usually a sign of increased platelet turnover, from destruction, consumption or an overactive marrow.
- Immune thrombocytopenia or other causes of rapid platelet destruction
- Infection, inflammation, or recovery from recent bleeding
- Myeloproliferative disorders or vitamin B12 / folate deficiency
- Cardiovascular and metabolic disease (modest, non-specific elevation)
A low PDW means platelets are unusually uniform in size — most often a normal finding, occasionally seen when the marrow is producing few new platelets.
- Normal variation (common)
- Reduced platelet production, e.g. aplastic anemia or marrow suppression by chemotherapy
When a PDW result needs attention
PDW alone rarely needs action. It matters when it accompanies an abnormal platelet count — easy bruising, nosebleeds, petechiae or prolonged bleeding with a low count, or a very high count — which should be reviewed by a clinician.
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PDW (Platelet Distribution Width) — frequently asked questions
- What does a high PDW mean?
- That platelets differ more in size than usual, which generally reflects faster platelet turnover: the marrow is releasing large young platelets to replace ones being used up or destroyed. Infections, immune conditions, recent bleeding and marrow disorders can all do this. A mildly high PDW with a normal platelet count is usually not significant.
- Is a low PDW anything to worry about?
- Rarely. Uniform platelet size is often simply normal for you. It becomes relevant only alongside a low platelet count, where it can suggest the marrow is not producing many new platelets.
- What is a normal PDW?
- Roughly 9–14% on most analysers, although the range depends on the machine and some report it in femtolitres instead. Compare with the reference range on your own report, and read it together with the platelet count and MPV rather than in isolation.
Related lab markers
- Hemoglobin →Hemoglobin is the protein in red blood cells that carries oxygen — low hemoglobin defines anemia.
- aPTT (Activated Partial Thromboplastin Time) →aPTT measures how many seconds your blood takes to clot through the “intrinsic” pathway — a core test for bleeding disorders and for monitoring heparin.
- Vitamin B12 →Vitamin B12 is essential for nerve function and red-blood-cell formation — a deficiency can cause anemia and neurological symptoms.
- All lab markers →Browse every biomarker guide in one place.
This page provides educational health information and does not replace professional medical advice, diagnosis, or treatment. Interpret any lab value with your clinician, who has your full medical context. For emergencies, contact emergency services.