Routine coagulation testing

Question 1

What are the 5 parts of the haemostat system

Answer 1

1. Blood vessels and vascular endothelium
2. Platelets
3. Coagulation factos- seal over breach in endothelium
4. Coagulation factors- dissolve clot
5. Fibrinolytic system

Question 2

What are the steps involved in clot formation

Answer 2

1. Clot initiation- platelet aggregation and activation of coagulation
2. Clot formation- Thrombin converts fibrinogen to fibrin as breach in vessel wall attracts platelets
3. Fibrinolysis- Activated platelets cause clot to form then clot is dissolved

Platelets are activated by 2VIIIa
Receptor G1p1b sticks to injured vessel wall to slow platelet down and activate it
Factor Xa helps activate clotting cascade

Question 3

Highlight the important factors involved in the clotting cascade

Answer 3

• Factors 7 and 5 work together to cause prothrombin cleavage to make thrombin
• Increase in thrombin leads to positive feedback to factors 2 and 8 to help strengthen clot
• Factor 13 converts fibrin to cross linked fibrin

Factor 12 doesn’t take part so you can be deficient in this and not bleed

Question 4

How is the clotting cascade regulated

Answer 4

• Anti-thombin III switches off the activation of clotting factors 9, 10, 11
• Protein C and S are vitamin K dependent anticoagulants and are therefore suppressed by Warfarin
• Factors 2,7,9,10 are also vitamin K dependent so also suppressed by warfarin

Question 5

What clinical signs would indicate a clotting disorder

Answer 5

• Epistaxis lasting more than 30 mins
• Menorrhagia >80mls
• Bleeding (prolonged) post surgery
• Drug and fam history

Exam: Purpura, Petechiae, soft tissue haematoma

Most common bleeding disorder will give you a normal coagulation screen

Question 6

What blood investigations would you carry out and what are the indications for a coag screen

Answer 6

FBC- plt count (may be normal is plt aren’t functioning)
-Coag screen- prothrombin time -Activated partial thromboplastin time -Fibrinogen

Indications for a coag screen

• Suspicion of bleeding disorder (VWD , Factor 8 deficiency)
• paracetamol overdose
• Liver disease- plt indicate severity
• Monitoring transfusion requirements

Question 7

What can cause variables in a coagulation screen

Answer 7

• Stress/ exercise (short APTT due to falsely elevated VIII - false reassurance)
• Excessive venous occlusion- tourniquet on for too long- Traumatic venepuncture
• Blood taken from in dwelling line (lines locked with heparin will give abnormal result)
• Dead space from butterfly line - ensure vacuette is filled to line
• Delayed transport to lab
• Patient haematocrit (Increased PCV will throw off citrate in bottle)

Question 8

What clotting problems are there in these findings

• Only a prolonged prothrombin time
• Prolonged PT and APTT

Answer 8

• Prolonged prothrombin time- Primary factor 7 problem- found in early warfarinisation, congenital factor 7 deficiency, early sepsis
• Prolonged PT and APTT- problems with clotting factor 2 (prothombin) and factor 5 & 10

Question 9

What clotting factors are affected by the extrinsic pathway

Answer 9

• Only factor 7 affected 1st as Factor 7 half life is only 90 mins
• Only prolonged PT
• Factor 7 deficiency - 1st few days of oral warfarin therapy -Sepsis -Congenital -Early vit K deficiency

Question 10

What clotting factors are affected by the common pathway

Answer 10

• Factors 2,5,10
• PT and APTT prolonged- PT more so
• Caused by Vit K deficiency, oral warfarin therapy , oral dabigatran
• Can be caused by disseminated intravascular coagluopathy- sepsis, meningitis
• malignancy - can directly activate factor 0

Question 11

What is the activated partial thromboplastin time

Answer 11

-Similar to PT but it is activated prothrombin time - the phospholipid used is specific for other clotting factors

-Refers to the intrinsic pathway - clotting factor 8,9, 11, 12
Causes:
-DIC -Liver disease -Massive transfusion -Unfractionated hepatic therapy
-Oral warfarin therapy -Heparin contaminated from line locks
-Anti-phospholipid syndrome - lupus anticoagulant
-Factor 8,9,11,12 deficiency

Question 12

What are factor 8 and factor 9 deficiency commonly called

Answer 12

• Factor 8 deficiency - Haemophilia A - X linked recessive
• Factor 9 deficiency - Haemophilia B- X linked recessive but rarer

*Factor 11 deficiency - jews *

Question 13

What is an APTT correction study

Answer 13

• Conducted when a patient has abnormal APTT
• Patient plasma mixed with normal plasma with all clotting factors at normal level
• If APTT corrects when normal plasma added then there is an underlying clotting factor deficiency

Question 14

What is a D-dimer and when is it used

Answer 14

• Breakdown product of a clot
• Indicated in
  
  • suspected DIC -Thrombolytic therapy assessment
  • Suspected VTE when used with a clinical prediction model like the Well’s score