Petechiae
People with leukemia may develop small, reddish spots on the skin that can be mistaken for rashes. These spots, also called petechiae [7], are most observable on the skin of the legs and buttocks. Petechiae is caused by a reduction in platelet count brought about by leukemia.
Platelets normally clump together and seal broken spots in the blood vessels to prevent blood leakage. They are responsible for helping the blood clot. The spots that mark petechiae are caused by the inability of platelets to do this. When small blood vessels, called capillaries, leak under the skin, the blood can appear on the skin surface as small spots.
One way to tell these spots apart from regular rashes is to use a “glass test”. Press a glass cup over the area of skin with the rashes. Normal rashes will turn pale or seem to disappear when seen through the glass. Spots caused by petechia will not. This method is not always accurate and shouldn’t always be relied on.