Epistaxis, or nosebleed, refers to a hemorrhage localized in the nose.

A reduction in the number of circulating thrombocytes.

Average platelet volume above the upper limit of the normal reference interval.

Abnormally increased variability in the size of platelets.

Abnormal platelet response to ADP as manifested by reduced or lacking aggregation of platelets upon addition of ADP.

Platelets contain contractile proteins (actin and myosin) that induce clot retraction. As the platelets contract, they pull on the surrounding fibrin strands, squeezing serum form the mass, compacting the clot and drawing the ruptured edges of the blood vessel more closely together. Clot retraction is directly proportional to the platelet count and inversely proportional to the fibrinogen concentration.