Clinical Interpretation of Low ADP on Platelet Mapping

Understanding ADP Measurement on Platelet Mapping

The European Society of Anaesthesiology recommends that platelet mapping using thromboelastography (TEG-PM) measures the percentage inhibition of the platelet P2Y12 receptor pathway, which is the specific target of ADP and medications like clopidogrel, prasugrel, and ticagrelor 1, 2
The American Heart Association notes that the test uses ADP as an agonist to stimulate platelet aggregation, and the degree of inhibition reflects how well the P2Y12 receptor pathway is blocked 3, 4
The European Heart Society states that low ADP inhibition means platelets are responding normally to ADP stimulation, suggesting the P2Y12 pathway is functional and not adequately blocked 5

The American College of Cardiology recommends that in patients on P2Y12 inhibitors (clopidogrel/prasugrel/ticagrelor), low ADP inhibition suggests inadequate platelet inhibition or "clopidogrel resistance", with various cut-off values proposed 3, 4
The European Society of Cardiology notes that this finding has been associated with 2-4 fold higher risk of myocardial infarction, stroke, or death in patients with cardiovascular disease 6
The European trauma guidelines (2023) recommend against routine use of POC platelet function devices including TEG-PM for monitoring trauma patients (Grade 1C recommendation) 1, 5

The American Society of Hematology states that different platelet function tests are not interchangeable and measure different parameters of platelet activation with different sensitivities 1, 2, 5
The International Society on Thrombosis and Haemostasis notes that results may be of limited value if platelet counts are low, as the test requires adequate platelet numbers to function properly 1, 5
The European Hematology Association states that correlation between different testing methods is only modest (66-78% agreement), meaning a patient may be classified as resistant by one method but responsive by another 7

The American College of Chest Physicians recommends that if patient is on clopidogrel with low ADP inhibition, verify medication compliance first before assuming pharmacologic resistance 6
The European Society of Cardiology notes that if patient is a trauma patient, do not rely on ADP inhibition results to guide platelet transfusion decisions given the poor performance and lack of established cut-offs 1, 5

The Anaesthesia society recommends continuing clopidogrel 75 mg daily without dose adjustment when ADP inhibition is therapeutic, and assessing bleeding risk factors, including age, prior bleeding history, and renal dysfunction, in patients with low ADP aggregation on TEG platelet mapping 8
For high bleeding-risk procedures, the Anaesthesia society suggests discontinuing clopidogrel 5 days before surgery to allow complete recovery of platelet function, based on platelet function testing to guide surgical timing 8
A strategy based on preoperative TEG platelet mapping to determine timing of CABG in clopidogrel-treated patients was associated with the same bleeding as clopidogrel-naive patients and 50% shorter waiting time than the standard 5 days, according to the Anaesthesia society 8
Patients in the higher tertile of platelet function inhibition measured by TEG platelet mapping had increased blood loss and transfusion requirements after coronary artery surgery, as reported by the Anaesthesia society 8
If bleeding occurs or urgent surgery is required, the Anaesthesia society recommends platelet transfusion as the only effective reversal strategy for clopidogrel's antiplatelet effect 8

In adults presenting with acute ischemic stroke, the speed of platelet inhibition varies by agent: cangrelor achieves immediate inhibition, prasugrel and ticagrelor have a rapid but slightly delayed effect, while clopidogrel shows the slowest onset; once administered, clopidogrel’s irreversible binding results in antiplatelet activity that persists for roughly five days after the drug is stopped. 9

Among patients with ischemic stroke, failure to disclose use of P2Y12 inhibitors (e.g., clopidogrel, prasugrel, ticagrelor) is common, so clinicians should not rely solely on the initial medication list; comprehensive reconciliation—including direct questioning, review of pharmacy records, and verification of any loading doses given in the emergency department—is essential to identify undisclosed therapy. 10