Haemostasis 3

Question 1

What does Prothrombin Time measure (PT)?

Answer 1

Extrinsic = VII

Common pathway = X, VI, II (prothrombin) and I (fibrinogen)

Question 2

What does the activated partial prothrombin time (APPT) measure?

Answer 2

Intrinsic pathway = XII, Xi, IX and VIII

Common pathway = X, V, II (prothrombin) and I (fibrinogen)

Question 3

What does the thrombin clotting time and Fibrinogen assay (TCT) measure?

Answer 3

I (Fibrinogen)

Question 4

What is the International Normalized Ratio (INR)?

Answer 4

Standardized commercial PT test results.

Ratio of patients PT to PT of normal plasma

Question 5

What is the reference range for the INR?

Answer 5

0.8-1.2

Question 6

What do coagulation assays measure?

Answer 6

Measured as a percentage of normal clotting activity - except fibrinogen

Question 7

List some causes of prolonged bleeding.

Answer 7

Defective vessel wall disorders
Platelet disorders (thrombocytopenia, defective platelet function)
Von Willebrand disease (low levels/abnormal vWF molecules, reduced platelet aggregation and prolonged bleeding)
Defective coagulation

Question 8

How do we assess bleeding disorders?

Answer 8

History - location of bleeding, pattern of bleeding, drug history and diet, family history

Question 9

What would be the lab assessments for bleeding disorders?

Answer 9

Blood screen - platelet count and morphology
Coagulation screen - PT, APTT, fibrinogen (TCT)

Second stage tests - vW factor assays, platelet function studies, coagulation factor assays

Question 10

What is Disseminated Intravascular Coagulation?

Answer 10

Widespread activation of platelets and coagulation in blood.

Question 11

What are the pathological processes behind DIC?

Answer 11

Release of procoagulant material into the circulation

Widespread focal or diffuse damage to endothelial cells

Question 12

What happens in mild DIC?

Answer 12

No adverse effects

Question 13

What happens in moderate/severe DIC?

Answer 13

Bleeding
and or
Thromboses and ischaemia

Question 14

Describe what happens in DIC.

Answer 14

Tissue factor/other cell products released in blood vessels or any cause of extensive endothelial cell damage 
Resulting in:
- platelet activation and aggregation
- activation of coagulation 
- formation of micro thrombi 
- secondary activation of fibrinolysis

Question 15

NB: fibrinolysis is always activated in DIC

Answer 15

Fibrin is cleared from the small blood vessels: high FDP levels produced
Inadequate activation results in microvascular thromboses

Question 16

What are the clinical findings of DIC?

Answer 16

Variable - those of the underlying condition

Bleeding and/or microvascular thromboses present if DIC is moderate/severe

Question 17

What the laboratory findings of DIC (consumptive coagulopathy)?

Answer 17

Falling fibrinogen concentration - prolonged TCT
Falling platelet count
High/rising level of fibrin degradation products (FDPs)
Reduced coagulation factors

Question 18

What diseases can cause DIC?

Answer 18

Gram negative septicaemia

Question 19

How do we treat DIC?

Answer 19

Treat the cause and DIC will stop: 
- infection = antibiotics
- trauma/shock = treat trauma/shock 
Secondary bleeding caused by DIC:
- replace with blood transfusion therapy

Question 20

What other disorders can cause DIC?

Answer 20

Any severe/widespread tissue injury 
- prolonged shock 
- extensive tissue trauma
- severe burns
- severe viral infections 
Traumatic brain injury with brain myelin (lipid) released into blood = activates platelets and coagulation

Question 21

What is the INR used for monitoring?

Answer 21

Warfarin coagulation

Question 22

What does a lack of vit K result in and why?

Answer 22

Lack of vitamin K results in bleeding

Factors II, VII, IX and X do not function normally

Question 23

What are common conditions causing vit K deficiency?

Answer 23

Liver disease
Newborn infants
Small bowel malabsorption disorders

Question 24

What is vit K?

Answer 24

Fat soluble vitamin

- vegetable sources and bacterial synthesis in colon

Question 25

What are some causes of vit K deficiency?

Answer 25

Low intake + antibiotics 
Malabsorption issues (bile salt issue, biliary tract obstruction) 
Liver stores of vit K

Question 26

Describe Vit K and Liver Disease.

Answer 26

Most coagulation factors are synthesized in the liver.
Severe liver disease results in reduced factor levels.
Vit K dependent factors decrease more than the others.
Injected doses of Vit K may improve coagulation status before a liver biopsy or surgery.
Long PT and APPT with a bleeding tendency

Question 27

Vit K and neonate.

Answer 27

Limited vit K transport across the placenta - risk of bleeding into the brain
Vit K is always given after birth
Premature infants - intramuscular dose of vit K

Question 28

What type of drug is Warfarin?

Answer 28

Anticoagulant - inhibits Vit K

Question 29

What are the benefits of Warfarin?

Answer 29

Useful for treating patients with pathologically increased risk of clotting
Oral medicine - injection not needed

Question 30

What are potential problems of Warfarin?

Answer 30

Risk of bleeding if excessive anticoagulation

Risk of clotting if insufficient anticoagulation

Question 31

What is important to note about the narrow therapeutic window for warfarin?

Answer 31

Careful clinical control is needed

Regular INR test (standardized prothrombin time)

Question 32

What are some common causes for Warfarin treatment to go out of control?

Answer 32

Changed intake of vit K in food
Decreased absorption of vit K
Change of medication
Any cause of liver cell injury