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Blood Test Tracker

Platelet Distribution Width (PDW)

A measure of how much the sizes of your platelets vary. It is a minor extra on some blood counts, and analyzers report it on different scales.

AI-verified against cited sources. Awaiting expert reviewAlso called PDW, PDW-SDLOINC 32207-3

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What it is

Platelets are small cell pieces that help your blood clot, and they are not all the same size. Platelet distribution width (PDW) measures how much their sizes vary. A higher PDW means a wider mix of small and large platelets. It comes from the analyzer that counts your blood cells, and not every lab reports it. Some analyzers report PDW in fL and others as a percent, so compare it only with the range printed on your own report.

Why it matters

PDW gives a small extra clue about how your platelets are being made and used. The spread in platelet size can widen when platelets are made or used up faster than usual, or when platelets are activated (switched on to form clots). By itself, PDW cannot point to a cause. Clinicians read it with your platelet count and MPV, which is the average platelet size.

If it’s high

A higher PDW means platelet sizes vary more than usual. This is often a minor finding, and usual ranges differ a lot between analyzers. A wider spread can be seen when platelets are being made or destroyed faster than usual. PDW has been linked to many conditions in studies, but it does not point to one cause on its own.

Common causes

  • Pregnancy, where PDW rose from the first to the third trimester in one study
  • Conditions that use up platelets faster than normal, such as immune thrombocytopenia (ITP)
  • Platelet activation, when platelets switch on to form clots
  • Giant platelets or platelet clumps that confuse the analyzer
  • Rare inherited platelet disorders that change platelet size, such as MYH9-related disease

What can help

  • Ask your clinician to read PDW together with your platelet count and MPV
  • Ask whether a blood smear is needed to look at your platelet sizes directly
  • If your result is far outside the range on your report, ask whether the CBC should be repeated

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 9.5–17.2 fL. Source: Scandinavian Journal of Clinical and Laboratory Investigation, Asian Journal of Transfusion Science.

What can affect your result

  • The analyzer: ranges differ widely, and some report fL while others report percent
  • Pregnancy: PDW rose across pregnancy in one study
  • How long the sample sat before testing: PDW fell with storage time in one study
  • Platelet activation, and how fast platelets are being made and used
  • Clumped or very large platelets, which analyzers can miscount
  • Age and sex: little effect in a study of 30,917 Danish blood donors
  • Analyzers report PDW on different scales (fL on some, percent on others) and with different ranges, so a result from one lab cannot be compared with another lab's range.
  • Sample age: in one study PDW fell the longer the blood sat before testing, while MPV rose.
  • Platelet clumps, platelets stuck to white cells, very large platelets and cell fragments can be miscounted by the analyzer, which also distorts the spread of platelet sizes.
  • A difficult blood draw or a refrigerated sample can trap platelets in small clots and cause clumping.

Platelets circulate for about 8 to 12 days, so PDW can shift over days to weeks as platelet production changes.

When to talk to a clinician

PDW on its own rarely needs urgent attention. What matters more is your platelet count. Contact your clinician promptly for unusual bleeding or bruising, such as nosebleeds or gum bleeding that is hard to stop, blood in your urine or stool, or many tiny red-purple dots on your skin. Call 911 or your local emergency number for heavy bleeding that will not stop, a sudden severe headache, or confusion.

Questions you could ask

  • Is PDW useful for me, or can I focus on my platelet count?
  • Is my platelet count in the usual range, and what is my MPV?
  • Does my lab report PDW in fL or percent, and which range should I use?
  • Would a blood smear or a repeat CBC add anything?

Questions people ask

Why is PDW in % on one report and in fL on another?

Different analyzers measure it in different ways and report it on different scales. A result in fL cannot be converted to a percent, or the other way round. Compare each result only with the range printed on the same report. The range shown here is for fL only.

Is PDW the same as MPV?

No. MPV is the average size of your platelets. PDW is how much their sizes vary. Two people can have the same MPV and a different PDW.

Should I worry about a slightly high PDW?

On its own, a small difference rarely tells much, and ranges vary by analyzer. Clinicians look at it with your platelet count and your other results. If you are unsure, ask your clinician whether it matters for you.

Show the science and sources

Units

  • 1 fL = 1 fL
  • 1 fL = 1 µm³

Is a change real?

PDW naturally varies about 3.43% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 11% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Systematic review and meta-analysis of within-subject and between-subject biological variation estimates of 20 haematological parameters (Coskun A et al., EFLM WG-BV).

For clinicians and researchers

PDW describes the width of the platelet size distribution measured by the analyzer. Scales differ by analyzer: LOINC has separate codes for PDW as a volume (fL) and as a ratio (percent), and published intervals appear in both. Intervals are analyzer-specific. A Sysmex XN-10 study of 30,917 Danish blood donors found 9.5 to 17.2 fL (2.5th to 97.5th percentile), stable across age and sex. A Sysmex XP-100i study of 1,634 Indian donors found 9.1 to 22.5 fL and listed other published intervals between 8.2 and 25 fL. In percent, 360 healthy Saudi adults on a Cell-Dyn Sapphire gave 14.9 to 17.9, and 253 healthy adults in Northern Sudan on a Sysmex KX-21 gave 14.73 to 16.10. This catalog gives no percent range, because percent and fL are different measures that cannot be converted into each other. The standard CBC reports of Labcorp, ARUP, Quest and Mayo Clinic Laboratories do not list PDW. PDW rises with platelet activation, and in one study it fell with sample storage time while MPV rose. Findings in thrombocytopenia are inconsistent: a 2024 study found higher PDW in destructive than in underproduction thrombocytopenia, while a study it cites found no difference.

LOINC 32207-3 (primary), 51631-0. Specimen: whole-blood.

Sources

  1. Reference intervals for platelet large cell ratio, platelet distribution width, plateletcrit and standard haematological parameters determined on the Sysmex XN-10 in a cohort of 30,917 Danish blood donors, Scandinavian Journal of Clinical and Laboratory Investigation (2022)
  2. Reference interval of platelet counts and other platelet indices in apparently healthy blood donors in North India according to Clinical and Laboratory Standards Institute guidelines: Need to redefine the platelet count cutoffs for repeat plateletpheresis donation?, Asian Journal of Transfusion Science (2022)
  3. Establishment of reference intervals for hematological parameters of adult population in the western region of Saudi Arabia, PLOS ONE (2023)
  4. Reference Intervals of Hematological Parameters Among Healthy Adults in Northern Sudan: A Community-Based Cross-Sectional Study, Journal of Clinical Laboratory Analysis (2025)
  5. Platelet distribution width: a simple, practical and specific marker of activation of coagulation, Hippokratia (2010)
  6. The Significance of Platelet Indices in the Evaluation of Thrombocytopenia, Cureus (2024)
  7. Mean Platelet Volume (MPV): New Perspectives for an Old Marker in the Course and Prognosis of Inflammatory Conditions, Mediators of Inflammation (2019)
  8. Diagnosis of Inherited Platelet Disorders on a Blood Smear, Journal of Clinical Medicine (2020)
  9. CBC with Platelet Count and Automated Differential (test 0040003), hotline effective March 1, 2021, ARUP Laboratories (2021)
  10. Complete Blood Count (CBC) With Differential, Reflex to Peripheral Smear Review (test 005009), Labcorp
  11. Platelet Count (test 005249), Labcorp
  12. CBC (includes Differential and Platelets) (test code 6399), Quest Diagnostics
  13. Complete Blood Cell Count (CBC) with Differential, Blood (test ID CBC), Mayo Clinic Laboratories

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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