Pathology Cheat Sheet
Build the Primary Plug
Primary haemostasis for NEET-PG: platelet plug, von Willebrand factor GpIb, ITP, von Willebrand disease, haemophilia A and B, and bleeding time vs PT vs aPTT.
MedNext Academy | 3 min read
Build the Primary Plug
Primary haemostasis for NEET-PG: platelet plug, von Willebrand factor GpIb, ITP, von Willebrand disease, haemophilia A and B, and bleeding time vs PT vs aPTT.
Normal haemostasis and the vascular and platelet disorders that impair the primary platelet plug, including ITP, von Willebrand disease, and haemophilia.
High-yield lines
- Primary haemostasis forms the platelet plug through vessel constriction, platelet adhesion, activation, and aggregation.
- Von Willebrand factor bridges platelets to exposed subendothelial collagen via the GpIb receptor.
- Platelet aggregation is mediated by fibrinogen binding to the GpIIb-IIIa receptor.
- Platelet-type bleeding causes mucocutaneous bleeding, petechiae, and prolonged bleeding time.
- Coagulation factor bleeding causes deep bleeds into joints and muscles with normal platelet count.
- Immune thrombocytopenic purpura is antibody-mediated platelet destruction, often against GpIIb-IIIa, with a normal or increased marrow megakaryocytes.
- Von Willebrand disease is the most common inherited bleeding disorder and prolongs the bleeding time and often the aPTT.
- Haemophilia A is X-linked factor VIII deficiency and haemophilia B is X-linked factor IX deficiency, both prolonging the aPTT.
- Haemophilia causes haemarthrosis and deep muscle bleeds with a normal prothrombin time.
- Bernard-Soulier syndrome is a GpIb defect and Glanzmann thrombasthenia is a GpIIb-IIIa defect.
- The bleeding time and platelet count assess primary haemostasis.
- The prothrombin time assesses the extrinsic pathway and the aPTT assesses the intrinsic pathway.
Mapped competency codes
- PA21.1
- PA21.2
- PA21.3
Continue into the full chapter
This summary maps to PA21-hemorrhagic-disorders.
Frequently Asked Questions
How does platelet-type bleeding differ from coagulation factor bleeding?
Platelet disorders cause mucocutaneous bleeding and petechiae with a prolonged bleeding time, while factor deficiencies cause deep joint and muscle bleeds with a normal platelet count.
What is the most common inherited bleeding disorder?
Von Willebrand disease, which impairs platelet adhesion and factor VIII stabilisation, prolonging the bleeding time and often the aPTT.
What is the inheritance and defect of haemophilia A?
It is X-linked recessive deficiency of factor VIII, causing haemarthrosis and deep muscle bleeds with a prolonged aPTT and normal prothrombin time.
What causes immune thrombocytopenic purpura?
Autoantibodies, often against platelet GpIIb-IIIa, that opsonise platelets for splenic destruction, with normal or increased marrow megakaryocytes.
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