Platelet distribution width (PDW) is a measure of the variation in size of platelets in the blood. It is typically reported as a percentage and is often included as part of a complete blood count (CBC) test.

PDW is related to mean platelet volume (MPV), which is a measure of the average size of platelets in the blood. PDW reflects the range of platelet sizes in the blood, whereas MPV reflects the average size.

An increase in PDW may indicate that there is a wider range of platelet sizes in the blood, which can be a sign of platelet activation or destruction. This may be seen in conditions such as immune thrombocytopenia, which is an autoimmune disorder that causes the destruction of platelets.

On the other hand, a decrease in PDW may suggest that there is a narrower range of platelet sizes in the blood, which can be a sign of decreased platelet production or abnormal platelet function. This may be seen in conditions such as thrombocytopenia, which is a decrease in the number of platelets in the blood, or in certain genetic disorders that affect platelet function.

Like MPV, PDW can be a helpful diagnostic tool, but it should be considered in the context of other clinical and laboratory findings to determine the underlying cause of any abnormalities in platelet size distribution.

see Platelet count.