Platelet Aggregation, ADP (Impedance)

This test assesses how well your platelets clump together when exposed to adenosine diphosphate (ADP), a chemical that normally triggers platelets to activate. It uses an impedance method, which measures changes in electrical resistance as platelets stick to electrodes in a blood sample. The more platelets aggregate in response to ADP, the greater the measured signal.

It is a functional platelet test, not a platelet count. It helps show whether your platelets respond appropriately to an ADP stimulus under standardized laboratory conditions.

Doctors use this test to evaluate unusual bleeding or bruising, to investigate suspected inherited platelet function disorders, and to assess the effect of medicines that block platelet ADP receptors. It may be ordered before surgery or procedures if there is a concern about bleeding risk, or to check how well certain antiplatelet treatments are working.

Abnormal platelet function can contribute to bleeding problems or, in some contexts, to a higher tendency for clotting. Understanding your platelet response to ADP can guide decisions about medication choice, dosing, timing around procedures, and whether more testing is needed to identify an underlying platelet disorder.

Results are interpreted alongside your medical history, medications, and other blood tests. Lower-than-expected aggregation can occur with medicines that inhibit the ADP pathway, with some inherited platelet receptor or signaling defects, or if the sample was not ideal. Higher-than-expected aggregation may suggest reduced effect of antiplatelet therapy or platelet hyperreactivity, but this finding must be interpreted cautiously.

If results do not match your clinical situation, your clinician may repeat the test, review sample handling, or add complementary platelet studies. Never stop or change antiplatelet medication without medical advice; decisions are individualized and balance bleeding and clotting risks.