Disorders of Primary and Secondary Hemostasis

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Overview

Hemostasis is the physiological process that stops bleeding after vascular injury while maintaining normal blood flow in intact vessels. It consists of two tightly connected phases: primary hemostasis, which leads to the formation of a platelet plug, and secondary hemostasis, which stabilizes this plug with fibrin. Disorders of hemostasis result in either excessive bleeding or pathological thrombosis.

Primary Hemostasis

Initiation, adhesion, activation and aggregation of platelets in primary hemostasis

Primary hemostasis involves the interaction between platelets and the damaged vessel wall. It includes three main steps:

• Vasoconstriction
• Platelet adhesion
• Platelet activation and aggregation

This process results in the formation of a temporary platelet plug.

Disorders of Primary Hemostasis

Disorders of primary hemostasis are characterized mainly by abnormal platelet number or function and defects of the vascular wall.

Quantitative Platelet Disorders (Thrombocytopenia)

Thrombocytopenia is defined as a decrease in platelet count below the normal range.

Main causes:

• Decreased platelet production (bone marrow suppression, leukemia, chemotherapy)
• Increased platelet destruction (immune thrombocytopenic purpura, drug-induced)
• Increased platelet consumption (disseminated intravascular coagulation)
• Splenic sequestration (hypersplenism)

Clinical manifestations:

• Petechiae
• Purpura
• Mucosal bleeding
• Epistaxis
• Menorrhagia

Qualitative Platelet Disorders (Thrombocytopathies)

These are disorders in which platelet count is normal, but platelet function is impaired.

Congenital causes:

• Glanzmann thrombasthenia – defect of platelet aggregation due to GpIIb/IIIa receptor abnormality
• Bernard–Soulier syndrome – defect of platelet adhesion due to GPIb-IX-V receptor abnormality

Acquired causes:

• Antiplatelet drugs (aspirin, clopidogrel)
• Uremia
• Liver disease

Clinical manifestations:

• Easy bruising
• Prolonged bleeding after minor injuries
• Mucosal bleeding

Vascular Disorders

These disorders are caused by increased fragility or damage of the vessel wall.

Examples:

• Ehlers–Danlos syndrome – hereditary collagen disorder
• Vitamin C deficiency (scurvy)
• Henoch–Schönlein purpura – immune-mediated vasculitis of small vessels
• Senile purpura

Clinical manifestations:

• Petechiae
• Purpura
• Easy bruising

Secondary Hemostasis

Coagulation cascade showing intrinsic, extrinsic and common pathways

Secondary hemostasis involves the coagulation cascade, where clotting factors are activated in a sequential manner, leading to the formation of fibrin which stabilizes the platelet plug.

It consists of:

• Intrinsic pathway
• Extrinsic pathway
• Common pathway

Disorders of Secondary Hemostasis

Disorders of secondary hemostasis are caused by deficiencies or dysfunction of coagulation factors.

Congenital Coagulation Disorders

• Hemophilia A – deficiency of factor VIII
• Hemophilia B – deficiency of factor IX
• von Willebrand disease – combined disorder affecting platelet adhesion and factor VIII

Clinical manifestations:

• Deep tissue bleeding
• Hemarthroses
• Muscle hematomas
• Delayed bleeding after trauma

Acquired Coagulation Disorders

• Vitamin K deficiency
• Liver disease
• Anticoagulant therapy (warfarin, heparin)
• Disseminated intravascular coagulation

Clinical manifestations:

• Extensive bleeding
• Internal hemorrhages
• Prolonged coagulation times

Differences Between Primary and Secondary Hemostasis Disorders

Feature	Primary Hemostasis	Secondary Hemostasis
Main defect	Platelets / vessels	Coagulation factors
Typical bleeding	Mucosal, skin	Deep tissues, joints
Petechiae	Common	Rare
Hemarthrosis	Rare	Common
Bleeding after trauma	Immediate	Delayed

Clinical Significance

Disorders of hemostasis can be life-threatening due to the risk of severe hemorrhage. Correct identification of whether the defect is in primary or secondary hemostasis is essential for correct diagnosis, laboratory testing, and treatment selection.

Sources

• Guyton and Hall – Textbook of Medical Physiology
• Robbins and Cotran – Pathologic Basis of Disease
• Stefan Silbernagl & Florian Lang – Color Atlas of Pathophysiology
• AMBOSS