PDW
What it measures, and what changes the number.
PDW stands for platelet distribution width. It describes how much platelets vary in size within a blood sample, calculated by the analyser from the spread of individual platelet volumes. It does not count platelets; it describes their size variation.
It is reported with the rest of the platelet indices in a complete blood count, mainly the platelet count, mean platelet volume (MPV) and plateletcrit. These are read together because size and variability give context to the count itself.
PDW is highly dependent on the analyser. Some instruments report it as an absolute width in femtolitres and others as a relative measure of spread, so results from different labs are often not comparable. Platelets can also swell over time in the collection tube, so delays before analysis affect the figure. Reports may show it as Amplitud distribució plaquetària.
Often read alongside: Platelets, MPV, Plateletcrit