Platelet function tests

Objective: Platelet function tests are recommended for patients when bleeding symptoms are not fully explained by standard laboratory investigations. In this report, we discussed ex vivo methods to evaluate platelet functions and and anti-platelet therapy. Methods: Light transmission aggregometry is the gold standart for evaluating platelet functions. In this method, in vitro platelet activation and aggregation is evaluated by using platelet agonists. The most fequently used agonists are adenosine diphosphate (ADP), arachidonic acid, kollagen, epinephrin, trombin and ristocetin. Multiplate analyzer (Roche) is based on impedans aggregometry in which activated platelets aggregate on trombogenic twin metal sensors and the increase in impedance is measured. Five different tests can be run at the same time in parallel such as aspirin, ADP, thrombin receptor-activating peptide (TRAP), collagen and ristocetin tests. Platelet function analyser (PFA-200) (Siemens) simulates primary hemostasis in vitro and widely used for in vitro bleeding time. Additionally, it can be used to detect inherited, acquired and drug-induced platelet dysfunction. Verifynow (Accumetrics) is an automated point of care system for the evaluation of platelet disfunctions due to anti-platelet therapy such as aspirin, ADP receptor antagonists and fibrinogen antagonists. The system measures the changes in light transmittance caused by platelets aggregating on fibrinogen coated plastic balls. Results: These systems for the assesment of platelet functions are becoming increasingly common either in laboratories or as point of care systems. Conclusion: The laboratories should select the best method for their purpose according to their localisation, requirement, the urgency and cost of the test.