From the Guidelines
Platelet function can be determined by lab tests such as aggregometry, VASP test, VerifyNow, and others.
Available Tests
These tests serve as surrogate markers for the clinical effectiveness of antiplatelet drugs and include:
- Conventional aggregation (photometric) which measures changes in light transmission in platelet-rich plasma 1
- Serum thromboxane B2 which measures thromboxane B2 in serum obtained from coagulated whole blood 1
- VASP test (vasodilator-stimulated phosphoprotein) which detects the degree of phosphorylation of the VASP protein by flow cytometry or ELISA 1
- VerifyNow which measures the consequence of the interaction between fibrinogen and activated GPIIb-IIIa complex in whole blood 1
- Aggregation detected by changes in impedance (e.g. Multiplate, ROTEM) which evaluates platelet function in whole blood 1
- PFA (Platelet Function Analyzer) which measures occlusion of an orifice in a membrane soaked with collagen and ADP or collagen and epinephrine 1
- TEG Platelet Mapping which evaluates the viscoelastic properties of whole blood and platelet involvement in clot formation 1
Clinical Use
While these tests are available, their clinical use is not well established, and there is little clinical information to document the desired haemostatic competence threshold 1. However, platelet function testing could be used with a possible small benefit and little harm in certain scenarios, such as patients undergoing CABG surgery who have recently started taking a P2Y12 inhibitor 1. The standard platelet function test is aggregometry, which measures ADP-stimulated platelet aggregation in whole blood or platelet-rich plasma 1. The VASP test and VerifyNow are more recent tests that quantify phosphorylation of vasodilator-stimulated phosphoprotein (VASP) in whole blood and appear to be more specific measures of clopidogrel-mediated inhibition of platelet aggregation 1. The choice of test may depend on the specific clinical scenario and the availability of the test. In general, point-of-care tests (POCT) such as VerifyNow and Multiplate may be useful in the perioperative setting to quickly assess platelet function 1. However, the use of these tests should be guided by clinical judgment and in coordination with the haemostasis team and the local medical laboratory 1.
From the Research
Lab Tests for Thrombocyte (Platelet) Function
Several lab tests can determine thrombocyte (platelet) function, including:
- Light transmission aggregometry (LTA) 2, which is considered the gold standard of platelet aggregation tests
- Flow cytometry-based methods 2, 3, which may be more convenient than LTA for studying patients with very low or very high platelet counts
- Platelet function analyzer (PFA-100) 3, 4, which is a good screening method to detect platelet function defects
- Rapid-Platelet-Function-Analyzer 3, which uses whole blood to measure glycoprotein (GP) IIb/III inhibitor activity
- VerifyNow System 4, which is a point-of-care testing (POCT) device for platelet function
- Multiplate Electrode Aggregometry (MEA) 4, which is another POCT device for platelet function
- Impedance aggregometry on whole blood 4, which is a laboratory test for platelet function
- Lumiaggregometry 4, which is a laboratory test for platelet function
Advantages and Disadvantages of Lab Tests
Each lab test has its advantages and disadvantages, and should be interpreted only in concert with a thorough history and physical examination 3. The ideal test should be simple, quick, inexpensive, and available on a 24-hour basis 3. Preanalytical factors, such as patient-related factors and selection of anticoagulant, can substantially affect test results 5.
Clinical Applications of Lab Tests
Lab tests for platelet function are used for various clinical purposes, including: