Assessment of platelet function: Laboratory and point-of-care methods

Table 1 Laboratory and point-of-care assays for evaluation of platelet function

Platelet function tests	Principle of method	Application of the methods
Platelet adhesion studies
Bleeding time	In vivo stopping of blood flow	Screening test of platelet function on defects of primary hemostasis
Platelet Function Analyzer - PFA-100/InnovancePFA-200	In vitro stopping of high shear blood flow by platelet plug in whole blood	Assessment of bleeding risk, thrombotic risk, drug effects Sensitive to severe platelet dysfunctions Detection of VWD
Impact Cone and Plate(let) analyzer	Shear-induced platelet adhesion/aggregation onto surface in whole blood	Screening of congenital primary hemostasis abnormalities Evaluation of platelet response to aspirin and clopidogrel (scarce data).
Platelet-To-Platelet Aggregation Studies
Light transmission platelet aggregation	Low shear platelet-to-platelet aggregation in response to agonists in platelet-rich-plasma	Screening test for bleeding behavior Diagnostic for platelet surface glycoprotein defects Monitoring of the platelet response to antiplatelet agents
Impedance platelet aggregation	Low shear platelet-to-platelet aggregation in response to agonists in whole blood	Screening test for bleeding behavior Diagnostic for platelet surface glycoprotein defects Monitoring of the platelet response to antiplatelet agents
VerifyNow system	Fibrinogen-platelet agglutination in response to agonist in whole blood	Monitoring of the platelet response to antiplatelet agents
Plateletworks	Platelet counting pre- and post-activation in whole blood	Monitoring of the platelet response to antiplatelet agents
Analysis of Clot Formation
Thromboelastography/ Thromboelastometry	Monitoring of rate and quality of clot formation in whole blood based on viscoelastic blood changes	Assessment of global haemostasis Possible definition of different platelet and clotting abnormalities Diagnosis and treatment of bleeding after cardiac surgery, liver transplantation, trauma and PPH
Platelet function tests to investigate platelet activation
Flow cytometry	Cell counting, cell sorting, biomarker detection and protein engineering laser-based detection of suspending fluorescent label platelets in a stream of fluid	Expression of platelet specific surface and/or cytoplasmatic markers; VASP phosphorylation state1 (Monitoring of CD41/61, CD42, CD62P, etc. Activation markers directly dependent on thienopyridine target)
Radio- or Enzyme Linked-Immune Assays: Soluble markers determination1	Ligand binding assays	Measurement of Beta-thromboglobulin, PF4, GPV, Soluble P-Selectin, Thromboxanes

¹Not planned in this report. GP: Glycoprotein; PPH: Post-partum hemorrhage; VASP: Vasodilator-stimulated phosphoprotein; VWD: Von Willebrand Disease.

Table 2 Advantages and disadvantages of different platelet function methodologies

Platelet tests	Advantages	Disadvantages
Bleeding time	Physiological In vivo test Easy, quick No WB processing	Operator dependent Invasive Poorly standardized Dependent on different variables (skin thickness, t°C)
Light transmission platelet aggregation in PRP	Historical gold standard Flexible Diagnostic method Different agonists available Sensitive for anti-plt therapy	Pre- and analytic variables Time-consuming High sample volume Sample preparation
WB Impedance Platelet Aggregometry	No sample preparation Flexible Diagnostic method Different agonists available Sensitive for anti-plt therapy Close to POCT (Multiple system)	Limited HCT and platelet count range
Flow Cytometry	Small blood volumes Diagnosis ex vivo of platelet activation Evaluation of efficacy of thienopyridyne therapy	Expensive Specialized equipment Experienced operator Careful sample processing Probable, possible artifacts
Platelet Function Analyzer -PFA-100 /Innovance PFA-200	In vitro standardized BT POCT Easy, quick Sensitive to severe platelet dysfunctions	Nonflexible Platelet count- HCT-dependent Not sensitivity for platelet secretion defects.
VerifyNow system	POCT WB assay Easy, quick No WB processing	Expensive Nonflexible Monitoring antiplatelet therapy only Limited HCT and platelet count
Impact Cone and Plate(let) analyzer	WB assay Global platelet function Small sample volume	Expensive Experienced staff Lacking of clinical studies Not widely available
Plateletworks	POC WB system Minimal sample preparation Easy, rapid screening test	Indirect assay Required platelet count method Not so well studied
Viscoelastic methods	POCT Global hemostasis test Anticoagulation monitoring Predicts bleeding Reduces blood transfusions Improve clinical outcome	Measure clot properties Depend on: platelet function, coagulation and fibrinolysis factors More studies are needed

HCT: Hematocrit; plt: Platelet; POCT: Point-of-Care Testing; PRP: Platelet-rich-plasma; WB: Whole blood.

Table 3 Major platelet function tests: Clinical value

Platelet tests	Clinical value	Ref.
Light transmission platelet aggregation	Assessment of: (1) idiopathic bleeding behavior (primary hemostasis defective); (2) residual platelet reactivity of patients on antiplatelet treatment to stratify risk of ischemic events; (3) detection of VWD (RIPA test); (4) diagnostic for platelet surface glycoprotein defects.	Moffat et al[34] Hayward et al[41] Gadisseur et al[43] Breet et al[44] Buonamici et al[45] Paniccia et al[51,65] Gum et al[63] Rechner[107]
Whole blood platelet aggregation	Assessment of: (1) idiopathic bleeding behavior (primary hemostasis defective); (2) residual platelet reactivity of patients on antiplatelet treatment to stratify risk of ischemic events; (3) acquired bleeding risk: antiplatelet therapy, surgical coagulopathy; (4) detection of VWD (RIPA test); (5) diagnostic for HIT.	Paniccia et al[72] Paniccia et al[73] Sibbing et al[74] Sibbing et al[75] Würtz et al[77] Bolliger et al[78] Morel-Kopp et al[79] Ranucci et al[81] Görlinger et al[84]
PFA-100 Innovance PFA-200	Assessment of: (1) idiopathic bleeding behavior (primary hemostasis defective); (2) detection of VWD; (3) acquired bleeding risk: anti-plt therapy, surgical coagulopathy; (4) thrombotic risk also in relation to potential failure of anti-plt therapy; (5) platelet function in pregnancy, kidney or liver disease.	Hayward et al[25] Favaloro[94] Koessler et al[92] Marcucci et al[103] Reny et al[104] Crescente et al[105] Raman et al[108] Cammerer et al[109] Chauleur et al[113]
VerifyNow system	Assessment of: (1) residual platelet reactivity of patients on antiplatelet treatment to stratify risk of ischemic events; (2) low platelet reactivity of patients on antiplatelet treatment to stratify risk of bleeding events (scarce clinical data).	Breet et al[44] Paniccia et al[51,65] Tantry et al[116] Marcucci et al[119] Price et al[120] Angiolillo et al[121]

HIT: Heparin-Induced Thrombocytopenia; plt: Platelet; RIPA: Ristocetin-Induced Platelet Aggregation; VWD: Von Willebrand Disease.