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Hemotology

Platelet Aggregation Studies

By Dayyal Dg.Twitter Profile | Updated: Thursday, 11 March 2021 22:30 UTC
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Platelet Aggregation Studies
Platelet Aggregation Studies

Platelet aggregation tests are carried out in specialized hematology laboratories if platelet dysfunction is suspected. These tests are usually indicated in patients presenting with the mucocutaneous type of bleeding and in whom screening tests reveal normal platelet count, prolonged bleeding time, normal prothrombin time, and normal activated partial thromboplastin time.

Platelet aggregation studies are carried out on platelet-rich plasma using an aggregometer. When a platelet aggregating agent is added to platelet-rich plasma, platelets form aggregates, and optical density falls (or light transmission increases); this is recorded by a chart recorder on a strip chart. Commonly used platelet aggregating agents are ADP (adenosine 5-diphosphate), epinephrine (adrenaline), collagen, arachidonic acid, and ristocetin. ADP (low dose) and epinephrine induce primary and secondary waves of aggregation (biphasic curve). The primary wave is due to the direct action of the aggregating agent on platelets. The secondary wave is due to thromboxane A2 synthesis and secretion from platelets. Collagen, arachidonic acid, and ristocetin induce a single wave of aggregation (monophasic curve) Normal aggregation curve is shown in Figure 804.1. Aggregation patterns in various platelet function defects are shown in Figures 804.2 to 804.4, and Table 804.1.

Normal platelet aggregation curves
Figure 804.1: Normal platelet aggregation curves
Platelet aggregation curves in von Willebrand disease and Bernard Soulier syndrome absent aggregation with ristocetin normal aggregation with ADP epinephrine and arachidonic acid
Figure 804.2: Platelet aggregation curves in von Willebrand disease and Bernard-Soulier syndrome (absent aggregation with ristocetin, normal aggregation with ADP, epinephrine, and arachidonic acid)
Platelet aggregation curves in storage pool defect absent second wave of aggregation with ADP and epinephrine absent or greatly diminished aggregation with collagen and normal ristocetin aggregation
Figure 804.3: Platelet aggregation curves in storage pool defect (absent the second wave of aggregation with ADP and epinephrine, absent or greatly diminished aggregation with collagen, and normal ristocetin aggregation)
Platelet aggregation curves in Glanzmanns thrombasthenia absent aggregation with all agonists except ristocetin
Figure 804.4: Platelet aggregation curves in Glanzmann’s thrombasthenia (absent aggregation with all agonists except ristocetin)
Table 804.1: Laboratory features of platelet function disorders
DisorderPlatelet Aggregation patternOther features
Bernard Soulier syndrome Normal with ADP, epinephrine, collagen, and arachidonic acid; deficient with ristocetin Autosomal recessive; severe bleeding; giant platelets
Glanzmann's thrombasthenia Deficient with ADP, epinephrine, collagen, and arachidonic acid; normal with ristocetin Autosomal recessive; severe bleeding; small and discrete platelets; defective clot retraction
Storage pool defect Primary wave with ADP and epinephrine, normal with arachidonic acid, deficient with collagen, normal with ristocetin Defects of platelets granules; platelet dense granules are decreased with the deficient release of ADP, ATP, calcium, and serotonin
Aspirin-like defect Primary wave with ADP and epinephrine, deficient with arachidonic acid, deficient with collagen, normal with ristocetin -
von Willebrand disease Normal with ADP, epinephrine, collagen, and arachidonic acid; deficient with ristocetin Autosomal dominant/recessive; abnormality in aggregation corrected with cryoprecipitate
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