What might cause petechiae during blood collection?

The formation of petechiae during blood collection is primarily associated with the application of a tourniquet that is too tight. When a tourniquet is applied, it temporarily restricts blood flow in the veins of the arm. If the pressure is excessive, it can lead to capillary rupture, resulting in small red or purple spots known as petechiae. This occurs because the increased pressure impairs venous return while still allowing arterial blood flow to continue, causing engorgement of the capillaries and subsequently leading to their rupture.

Other factors such as the depth of the needle, the speed at which it is withdrawn, and the gauge of the needle typically have less direct influence on the immediate formation of petechiae compared to the effect of an overly tight tourniquet. While those factors can contribute to discomfort or other complications, the primary cause of petechiae is related to capillary pressure and damage when tourniquet pressure exceeds normal levels.