Platelet distribution width

Platelet distribution width (PDW) describes how much the size of circulating platelets varies from one to another. It is reported on the full blood count as a companion to the platelet count and mean platelet volume rather than as a stand-alone measure.

Like other platelet indices it depends on the analyser and on how the sample was handled: clumping in the tube can disturb platelet measurements, and laboratories often comment or ask for a repeat.

PDW is interpreted with the platelet count and MPV, not alone. Wider variation in platelet size can accompany inflammation, iron deficiency or marrow stress, but small shifts in well people are common and often mean nothing on their own.

This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.

Platelet size varies with how quickly the marrow is releasing them, so the spread of sizes reflects platelet turnover rather than how well the platelets work. It does not replace a clinical assessment of bleeding or clotting.