ClinLab NavigatorPlatelet Function Screen

Enhancing Platelet Dysfunction Diagnosis with Platelet Function Screen

The Platelet Function Screen (PFA-100®) is a critical in vitro system for detecting platelet dysfunction. It uses citrated whole blood samples under high shear flow conditions, demonstrating its sensitivity. As blood is aspirated through collagen-coated membranes, platelet adhesion forms an initial matrix. Adding to the mix, platelet aggregation is stimulated by either epinephrine (COL/EPI) or adenosine diphosphate (COL/ADP), coating the membranes.

In this process, the time required to form a platelet plug that blocks the aperture, known as closure time (CT), is the key measure of platelet function. Interestingly, several conditions can cause prolonged CT, including drug effects, low hematocrit, thrombocytopenia, von Willebrand Disease (vWD), and platelet disorders. Notably, aspirin therapy impacts the COL/EPI closure time more than COL/ADP.

While assessing results, hematological considerations are pivotal, particularly with anemia and thrombocytopenia that could extend CT. Platelet counts below 150,000/uL or hematocrit below 35% could interfere with the results, thus, the test might not serve patients with counts below 100,000/uL or hematocrit under 30%. Moreover, hematocrit over 50% could generate inconsistent outcomes.

Fundamentally, normal CT with both COL/EPI and COL/ADP signifies healthy platelet function. The COL/EPI membrane, while sensitive to primary hemostasis disorders, lacks specificity. It could reflect thrombocytopenia, anemia, antiplatelet medication, or mild platelet dysfunction if CT is prolonged. Additionally, the PFA-100 screen identifies platelet dysfunction due to aspirin or aspirin-like drugs but not antiplatelet medications like clopidogrel or ticlopidine.

Meanwhile, normal CT with COL/EPI but prolonged with COL/ADP could indicate von Willebrand disease or certain platelet aggregation disorders. PFA-100 is particularly sensitive to vWD subtypes and inherited platelet function defects. However, it is less sensitive for diagnosing types 1 and 2B vWD, for which further tests are required.

Generally, random pre-operative screening isn’t advisable with the Platelet Function Screen. It’s most beneficial for patients with a history suggestive of hereditary or acquired platelet dysfunction, or vWD. Lastly, it’s crucial to send the sample to the laboratory within 3 hours of collection for accurate results.