Cogulation

Question 1

What is the anticoagulant used and why?

Answer 1

Sodium citrate dihydrate (3.2%?)
Ratio of blood:anticoagulant = 9:1
Citrate chelates free calcium ions which prevents coagulation

Question 2

Where are the coagulation factors made?

Answer 2

Liver

Question 3

Outline the principle of the ACL TOP 550?

Answer 3

The time taken for Fibrin clot formation
Measures the amount of light that can pass through the sample
A reduction in the amount of light determines the point of clot formation

Question 4

Outline the principle of the prothrombin time test

Answer 4

This test is based on the principle that in citrated (anticoagulated) plasma, the addition of a thromboplastin (Recombiplastin) (and CaCl2?) allows for formation of a stable clot
Thromboplastin acts on factor Xa and allows for the conversion of prothrombin to thrombin
The time taken for aclot to form is known as the prothrombin time
PT looks at the extrinsic pathway

Question 5

Outline the principle of the activated partial thromboplastin time test

Answer 5

APTT test looks at the intrinsic pathway of coagulation
In citrated plasma, the addition of a platelet substitute, factor XII activator, and CaCl2 allows for formation of a stable clot
The synthasil reagent activates APTT (the intrinsic pathway) while the addition of CaCl2 triggers coagulation to begin.
The time required for clot formation is measured.
1L synthasil APTT activator + test + CaCl2

Question 6

Outline the principle of the fibrinogen test

Answer 6

Fibrinogen C (Clauss fibrinogen) reagent contains thrombin which converts fibrinogen to fibrin
The time taken for fibrin clot to form is then measured

Question 7

Outline the principle of the D-Dimer test

Answer 7

D-dimer measured using latex agglutination and immunoenzymatic methods
D-dimer is detected using monoclonal antibodies bound to latex beads
The d-dimers are fibrin degradation profucts
Latex particles coupled to a monoclonal antibody specific for d-dimers (agglutination between latex beads facilitated by presence of d-dimers)

Question 8

What are the causes of a prolonged APTT

Answer 8

Factor deficiencies -which ones due to liver failure
Heparin therapy
Acquired inhibitors
Lupus anticoagulant
DIC
Heparin contamination

Question 9

How is INR calculated?

Answer 9

[Patient PT/mean of normal PT] ISI

INR = International normalised ratio

ISI =

Question 10

What results are expressed in time (secs)?

Answer 10

PT
APTT
TT

Question 11

What results are expressed in ratio?

Answer 11

APCR-V = activated protein C resistance (factor V leiden)
Lupus = lupus anticoagulant

Question 12

What results are expressed in %?

Answer 12

AT
PC
Free PS

Question 13

What results are expressed in IU/ml?

Answer 13

Anti-XA

Question 14

What is the mode of action of Dabigatran?

Answer 14

Dabigatran is a reversible direct thrombin inhibitor
It has a predictable anticoagulant effect but does not need as tight monitoring like warfarin
It binds to thrombin which prevents thrombin-mediated activation of coagulation factors

Question 15

What is the mode of action of Rivaroxaban?

Answer 15

Rivaroxzban competitively inhibits free and clot bound factor Xa
Without Xa prothrombin (F2) cannot be converted into thrombin (2a) and thus fibrinogen cannot be converted to fibrin

Question 16

What is the mode of action of Apixaban?

Answer 16

Inhibits free and clot-bound Xa, inhibits prothrombinase activity which inhibits clot growth

Apixabin decreases thrombin generation and thrombus development-> this has a knock on affect on platelet aggregation

Question 17

What would you do with a normal PT but prolonged APTT?

Answer 17

Check for clot
Check HCT - do they need an adjusted citrate bottle
Check if patient on heparin
Lupus anticoagulant test
Factor deficiencies of the intrinsic pathway
Correction studies? - mixing studies? 50:50 mix normal plasma + patient plasma

Question 18

What factors are involved in the extrinsic pathway

Answer 18

Factors VII, X, V, II (Prothrombin) and Fibrinogen

Question 19

What factors are involved in the intrinsic pathway

Answer 19

factors XII, XI, IX, and VIII.
8,9,11,12