Reversible platelet aggregation in the presence of calcium ions: mechanisms and potential value

Abstract

Disorders in the functions of platelets – blood cells responsible for the blood clots formation and prevention – are observed as independent diseases, as a complication of cancer and hematological diseases or as a result of a therapy. Nowadays, a test of platelet aggregation by aggregometry is the only diagnostic method for assessing the platelets functions. There are several varieties of aggregometry, which differ both in the method of recording the formation of platelet aggregates and in the method of preparing platelets for the experiment. In most laboratories, it is customary to conduct aggregometry in platelet-rich plasma in the presence of citrate ions. In this case, the concentration of calcium ions in plasma decreases, it prevents the thrombin formation and the plasma coagulation. On the other hand, it has long been known that platelet aggregation in response to ADP in the presence of calcium ions (in blood plasma collected in heparin or hirudin tubes, also blocking plasma clotting) is reversible: after 1-5 minutes after the addition of the activator, the disaggregation begins until the light transmission of the solution (platelet concentration) returns to its original level. This phenomenon is called "reversible” platelet aggregation. Reversible aggregation (“disaggregation”) is sometimes observed in aggregometry of citrate plasma, especially in pediatric patients. However, it is usually not considered normal and is considered a sign of platelet dysfunction. This review considers the known mechanisms of disaggregation in the presence or absence of calcium ions in the medium. The role of secondary activation of platelets as a potential cause of irreversible aggregation is discussed, as well as possible versions for explaining the results of aggregometry, when reversible platelet aggregation is observed.