Background

Platelet play an important role in immunological response, inflammation, development of tissue, and control the bleeding. When there some injury and if the bleeding is occur, platelet comes to the site and build a clot which prevent the further blood loss. This process is known as platelet aggregation.  

A platelet aggregation test is used to evaluate the ability of the platelet to form the proper clot. Any dysfunction in platelet aggregation may lead to excessive bleeding. The PAT test evaluate the aggregation reaction of platelets to different platelets activators like thrombin, ADP, arachidonic acid, collagen, ristocetin, and epinephrine by the use of light transmission aggregometer.  

Pat test is important to detect the bleeding diseases, monitor antiplatelet medications, and assess the abnormal function of platelet which can be acquired or inherited. This test is used to diagnose genetic platelet function diseases like Glanzmann thrombasthenia, dysfunction in acquired platelets because of drugs like clopidogrel or aspirin, and von Willebrand disease. 

Indications/Applications

Platelet aggregation test is performed in the following conditions like: 

To diagnose the platelet function disease, which can lead to excessive bleeding 

To monitor the antimicrobial treatment: to evaluate the effectiveness of antiplatelet drugs to prevent thrombotic events.  

Pre-surgical evaluation: Before the surgery, to check any history of bleeding or antiplatelet treatment 

Examine thrombocytopenia: To differentiate between qualitative and quantitative disorders of platelets.  

Evaluate the function of platelets in conditions like uremia, liver disease, and myeloproliferative diseases. 

Symptoms like excessive brushing or bleeding, bleeding from gums and nose, excessive menstrual bleeding, or blood in stool or urine. 

Reference Range

The normal results of this test may differ from laboratory to laboratory and which agonist is being used. It shows a typical biphasic aggregation pattern as per the particular agonists. 

ADP: It causes biphasic reaction. The 1st phase is tiny and rapid aggregation. The 2nd phase is bigger and prolonged because of the thromboxane A2 is released. 

Collagen: It causes fast and prolonged one-phase aggregation because collagen receptors are directly activated on platelets. 

Ritocetin: It increases a particular cluster by VWF factor> this can lead to medium and fast aggregation. 

Arachidonic acid: It increases the slow aggregation process by the pathway of thromboxane A2.  

Epinephrine: It causes mild and irregular aggregation by alpha-adrenergic receptors. 

Aggregegogram abnormalities may suggest different platelet function diseases. 

Hypersensitivity: Rapid aggregation suggests hyperactivity of platelet. 

Hyposensitivity: Slow or absence of aggregation suggests impaired function of platelets. 

Delayed aggregation: This may suggest abnormality in particular pathways in the platelets. 

No 2nd phase: This suggests a defect in the pathway of thromboxane A2 production. 

Interpretation

Normal aggregation suggests normal function of platelets.  

Reduced aggregation linked to conditions like products of fibrin degradation, Bernard-Soulier syndrome, autoimmune disease which produce antiplatelet antibody, Glanzmann thrombasthenia, uremia, myeloproliferative diseases, medications which block the formation of platelets, and von Willebrand disease 

Elevated aggregation is rare but seen in hyperactive function of platelet. No aggregation is linked to severe dysfunction in platelet or there is presence of antiplatelet agent. 

Collection And Panels

Sample type: Whole blood 

Sample collection method: Routine venipuncture 

Sample collection container: light blue vacutainer 

Sample volume: 4 mL 

Considerations: The platelet aggregation test needs 4 tubes. To perform a secretion test and full aggregation test, 7 tubes are needed. Whole blood sample must be processed in 4 hours after the collection. Sample must be stored in the room temperature. 

Panels: 

Complete blood count (CBC) test 

Prothrombin time 

Platelet count 

Partial thromboplastin time 

Coagulation factor 

Bone marrow biopsy 

von Willebrand factor 

Modifying factors: 

Over the counter (OTC) medications may affect the results of PAT test. This includes medications like: 

Aspirin or a compound which contain aspirin  

Tricyclic antidepressants 

Antibiotics like cephalosporins, penicillin, nitrofurantoin 

Antihistamine 

Dipyridamole 

Theophylline  

Nonsteroidal anti-inflammatory medications 

Clopidogrel 

Ticlopidine 

Other technical factors which may interfere with the results are improper preparation of PRP, variations in temperature, concentration of agonists, and calibration of instrument. 

References

https://www.ncbi.nlm.nih.gov/books/NBK53449/