Platelets are small, cell-like particles produced in the bone marrow. They function to start the formation of blood clots. Platelets gather where bleeding occurs and clump together to form the initial plug that stops or slows the flow of blood. Platelets also release substances that are needed to complete the clotting process.

Platelet disorders can result from having too few or too many platelets or from impaired platelet function. In general, when platelet counts fall very low there is an increased risk of bleeding. Decreased numbers of platelets may be caused by autoantibodies, drugs, toxins, or disorders of the bone marrow.

An abnormal increase in the number of platelets is rare and often the cause is not known. It may be associated with bone marrow disease or with longterm blood loss and iron deficiency.

There are also disorders in which platelets do not function properly. Von Willebrand disease is one example. Other hereditary disorders of platelet function have been described but are rare. Probably the most common platelet function defect in animals is a side effect of aspirin. Do not give your dog aspirin—or any other medication—unless it is prescribed by your veterinarian.

Last full review/revision July 2011 by Peter H. Holmes, BVMS, PhD, Dr HC, FRCVS, FRSE, OBE; Nemi C. Jain, MVSc, PhD; David J. Waltisbuhl, BASc, MSc; Michael Bernstein, DVM, DACVIM; Karen L. Campbell, MS, DVM, DACVIM, DACVD; Timothy M. Fan, DVM, PhD, DACVIM; Wayne K. Jorgensen, BSc, PhD; Sarah E. Payne, DVM, DACVIM