Assessing Haemostasis

Questions and Answers

What is the primary function of thrombin in the coagulation process?

It breaks down fibrin into fibrin split products.

It activates platelets for aggregation.

It inhibits fibrinolysis.

It converts fibrinogen to fibrin. (correct)

Which step is NOT involved in normal haemostasis after blood vessel injury?

Platelet adhesion

Collagen exposure

Fibrinolysis activation (correct)

Platelet aggregation

What is a common consequence of arterial thrombosis?

Venous insufficiency

Myocardial infarction (MI) (correct)

Deep vein thrombosis (DVT)

Pulmonary embolism

What characterizes a bruise (haematoma)?

It involves micro/macroscopic tearing of blood vessels. Signup and view all the answers

Which receptor type is NOT typically found on platelets?

Nuclear Hormone Receptors Signup and view all the answers

What role does plasmin play in the process of fibrinolysis?

It breaks down fibrin into fibrin split products. Signup and view all the answers

What is the result of inappropriate stimulation of platelets?

Thrombosis Signup and view all the answers

What color change indicates the presence of biliverdin in a bruise?

Green Signup and view all the answers

What commonly causes deep vein thrombosis (DVT)?

Deficiencies in inhibitors of coagulation factors Signup and view all the answers

What condition is characterized by a deficiency in platelet count?

Thrombocytopenia Signup and view all the answers

Which clinical feature is commonly associated with both primary haemostatic disorders and coagulation disorders?

Epistaxes Signup and view all the answers

What type of bleeding is typically immediate in primary haemostatic disorders?

Petechiae Signup and view all the answers

Which investigation measures the time it takes for bleeding to stop following a small incision?

Bleeding Time Signup and view all the answers

What clinical feature is uncommon in primary haemostatic disorders but common in coagulation disorders?

Haemarthroses Signup and view all the answers

Which factor is NOT assessed by PFA-100?

Blood cell morphology Signup and view all the answers

What typically indicates abnormal bleeding from weak blood vessels?

Vascular defects Signup and view all the answers

In typical cases, which gender is more frequently affected by coagulation disorders?

Primarily male Signup and view all the answers

Which test is modernly used to assess platelet function in response to a wound?

PFA-100 Signup and view all the answers

What is the normal bleeding time range?

3-8 minutes Signup and view all the answers

What initial interaction occurs between platelets and damaged blood vessel sites?

vWF binds to collagen and the GPIb complex on platelets. Signup and view all the answers

What occurs after platelets begin rolling along collagen?

GPVI receptor initiates a signaling cascade increasing intracellular calcium. Signup and view all the answers

How does the fibrinogen receptor contribute to the formation of a platelet plug?

It enables cross-linking of platelets through binding to fibrinogen. Signup and view all the answers

What is the primary role of fibrinogen in platelet plug formation?

To increase local concentrations and aid in coagulation. Signup and view all the answers

What is the abundance of the fibrinogen receptor on the surface of a platelet?

It is about 80,000 copies per platelet. Signup and view all the answers

What analogy is used to describe the abundance of the fibrinogen receptor on platelets?

Each person in a stadium holding hands with another in a different stadium. Signup and view all the answers

Which receptor on platelets binds to collagen and initiates the activation process?

GPVI Signup and view all the answers

What is the effect of increased intracellular calcium in activated platelets?

It causes a shape change and granule secretion. Signup and view all the answers

What does the PFA-100 primarily replace in platelet function assessment?

Bleeding time Signup and view all the answers

Which of the following is NOT one of the five common external aggregating agents used in platelet aggregation studies?

Thrombin Signup and view all the answers

What is the primary purpose of measuring serum thromboxane in patients taking aspirin?

To determine resistance to aspirin Signup and view all the answers

How is the International Normalized Ratio (INR) calculated?

(Patient PT / Normal PT) × ISI Signup and view all the answers

Activated Partial Thromboplastin Time (aPTT) is primarily used to assess which pathway of coagulation?

Intrinsic pathway Signup and view all the answers

What potential problem can arise from differences in thromboplastin potency when monitoring warfarin?

Inconsistent INR values across hospitals Signup and view all the answers

What is the normal range for Prothrombin Time (PT) in seconds?

11-16 seconds Signup and view all the answers

Which test is most appropriate for monitoring patients on heparin therapy?

Activated Partial Thromboplastin Time (aPTT) Signup and view all the answers

What mechanism does aspirin use to reduce platelet activity?

Inhibiting thromboxane A2 production Signup and view all the answers

Which test can be described as a non-invasive method to determine aspirin resistance?

AspirinworksÒ urine test Signup and view all the answers

What is the typical range for the Activated Partial Thromboplastin Time (aPTT)?

30-40 seconds Signup and view all the answers

Which anticoagulants are increasingly replacing warfarin for the treatment of DVT and PE?

Rivaroxaban and Apixaban Signup and view all the answers

What does the Thrombin Time assess in coagulation?

Fibrinogen conversion to fibrin Signup and view all the answers

What happens to the aPTT when a patient's plasma is diluted in normal plasma?

It should correct prolonged clotting times Signup and view all the answers

What could elevated D-dimer levels indicate?

Recent venous thrombosis Signup and view all the answers

How is a PCR used in the context of bleeding disorders?

To amplify DNA for genetic testing Signup and view all the answers

What is the normal range for Thrombin Time?

15-19 seconds Signup and view all the answers

What is indicated if the patient plasma shows prolonged clotting times after incubation with normal plasma?

Presence of coagulation factor deficiency Signup and view all the answers

What is likely to happen if fibrin split products are present in the bloodstream?

They block platelet activation Signup and view all the answers

Which of the following is NOT assessed by a D-dimer assay?

Fibrinogen levels Signup and view all the answers

Study Notes

Steps of Haemostasis

Five key steps: vessel spasm, platelet plug formation, coagulation, clot retraction, fibrinolysis.

Initial Platelet Interaction

vWF (von Willebrand factor) binds collagen exposed at damaged sites and the GPIb complex on platelet surfaces, slowing platelet movement.

Platelet Activation Process

Platelet rolling occurs as GPVI receptor binds collagen, triggering a signaling cascade that increases intracellular calcium.
Increased calcium leads to granule secretion, conversion of αIIbβ3 to a high-affinity state, and changes in platelet shape.

Fibrinogen Role in Platelet Plug Formation

Converted fibrinogen receptor (αIIbβ3) on platelets binds fibrinogen, cross-linking platelets to form a stable plug.

Fibrinogen Receptor Abundance

Approximately 80,000 copies of the fibrinogen receptor (αIIbβ3) exist on each platelet, facilitating effective platelet aggregation.

Analogy for Fibrinogen Connectivity

A comparison to individuals linking hands across multiple Millennium Stadiums illustrates the extensive connectivity provided by abundant receptors.

Types of Platelet Receptors

Platelets contain various receptors: Receptor Tyrosine Kinases (RTKs), G Protein-Coupled Receptors (GPCRs), and Integrins, each serving unique functions in activation and signaling.

Coagulation Process

Coagulation transforms fluid blood into a gelatinous clot, stabilizing the platelet plug.
Thrombin converts prothrombin to thrombin, then converts fibrinogen to fibrin.

Fibrinolysis

Plasminogen is activated to plasmin, leading to the breakdown of fibrin and the resolution of clots.

Causes of Bleeding Disorders

Result from deficiencies in platelet number/function or coagulation factors.

Causes of Thrombosis

Arterial thrombosis arises from inappropriate platelet stimulation, such as ruptured atherosclerotic plaques.
Venous thrombosis is often due to a lack of coagulation inhibitors.

Normal Haemostasis Steps

Sequence includes collagen exposure, platelet adhesion, activation, secretion, aggregation, and ultimately, platelet plug formation.

Outcome of Normal Haemostasis

Successful formation of a platelet plug at the injury site, crucial for preventing excessive bleeding.

Consequences of Arterial Thrombosis

Can lead to myocardial infarction (MI), ischemic stroke, and peripheral artery disease (PAD).

Venous Thrombosis Consequence

Primarily causes deep vein thrombosis (DVT) with clot formation in the veins, typically in the legs.

Thrombotic Pathology Mechanism

Stable clot formation disrupts normal blood flow, can occur in arteries or veins, and involves coagulation activation.

Signs and Symptoms of Thrombotic Disorders

Symptoms vary by location: chest pain for coronary arteries, FAST sequence for carotid arteries, unilateral leg pain for deep vein thrombosis.

Bruise (Haematoma) Characteristics

Result from blood vessel tearing, showing color changes as blood is phagocytosed and degraded over time.

Colour Changes in Bruises

Red-blue indicates haemoglobin, green signifies biliverdin, yellow indicates bilirubin, and golden represents hemosiderin.

Haematoma Definition

Purple/red discoloration caused by bleeding under the skin.

Types of Haematomas

Petechiae: small spots (1cm or less), larger hematomas represent pooling in the tissue.

Vascular Defects

Abnormal bleeding can occur from weak vessels that leak.

Thrombocytopenia

A deficiency of platelets that leads to abnormal bleeding.

Disorders of Platelet Function

Abnormal bleeding stemming from dysfunction of platelet components.

Coagulation Issues

Abnormal bleeding can arise from coagulation process deficiencies.

Clinical Features of Bleeding Disorders

Common clinical features include bleeding, petechiae, and epistaxis for primary and coagulation disorders; menorrhagia and haemarthroses distinguish primary from coagulant disorders.

Investigation Process in Haemostatic Disorders

Involves personal and family medical history, risk factor assessment, and blood tests.

Full Blood Count (FBC)

Provides data on the number and types of blood cells present.

Bleeding Time

Normal range: 3-8 minutes. Observes how long it takes for bleeding to stop after a small incision.

PFA-100

Modern test evaluating platelet function and plug formation using citrated blood.

Platelet Aggregation Studies

Measure light absorbance drop in platelet-rich plasma during aggregation using agents such as ADP and collagen.

Flow Cytometry

Analyzes platelet surface proteins, increasingly used to identify defects.

Serum Thromboxane Levels

Reflect thromboxane involved in platelet activation; reduced levels indicate aspirin's antiplatelet effect.

Aspirin Usage

Commonly prescribed for reducing platelet activity to prevent arterial thrombosis.

Coagulation Assays

Include Prothrombin Time (PT) and Activated Partial Thromboplastin Time (aPTT), used for monitoring bleeding disorders and anticoagulant therapy.

INR (International Normalized Ratio)

Used to standardize PT results for warfarin therapy; normal ~1.0, therapeutic ranges vary based on condition treated.

Thrombin Time

Evaluates how quickly fibrinogen converts to fibrin; normal range is 15-19 seconds.

Factor Assays

Measure activity of specific coagulation factors; prolonged clotting time identifies deficiencies.

D-dimer Assays

Elevations indicate the presence of thrombus; useful in diagnosing conditions like DVT.

PCR Testing

Detects genetic abnormalities associated with bleeding disorders, allowing for pedigree, phenotype, and genotype analysis.

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Description

Test your knowledge on the coagulation process and haemostasis with this quiz. Explore essential components such as thrombin's function, the steps of normal haemostasis, and the role of plasmin in fibrinolysis. Challenge yourself to identify key characteristics of bruises and the types of receptors present on platelets.