Coagulation tests

Question 1

What pathway is affected if only APTT prolonged

Answer 1

Intrinsic or common

Question 2

What pathway is affected if only PT prolonged

Answer 2

Extrinsic

Question 3

What pathway is affected if both APTT and PT prolonged

Answer 3

Common pathway

Question 4

What factors are part of intrinsic pathway

Answer 4

12,11,9,8
Count down from 12 missing 10

Question 5

What factor represents extrinsic pathway

Answer 5

VII/7

Question 6

Common pathway factors

Answer 6

I,II,V,X

Question 7

What factor joins extrinsic and intrinsic pathways

Answer 7

X

Question 8

Clotting cascade end

Answer 8

X+V - Ca2+ + lipids -> thrombin –prothrombin –> fibrinogen -> fibrin clot

Question 9

Causes of isolated prolonged PT

Answer 9

Isolated vit K deficiency (early stages)
Liver disease (early stages)
Warfarin in therapeuti range - INR
Congenital and acquired FVII deficiency

Question 10

Prolonged APTT

Answer 10

Lupus anticoagulant - misnomer
Unfractionated heparin
Congenital intrinsic factor deficiency
Acquired intrinsic factor inhibitors/acquired haemophilia

Question 11

What is lupus anticoagulant

Answer 11

Misnomer - prolongs APTT
Not ass w increased bleeding risk - increased VTE risk
Ass transient transfusion, SLE, antiphospolipid syndrome

Question 12

What factor deficiency causes haemophilia A

Answer 12

FVIII

Question 13

What facotr deficiency causes haemophilia B

Answer 13

FIX

Question 14

How to test for factor deficiencies singular vs multiple

Answer 14

50:50 mix blood test
1:1 patient blood and normal blood

Question 15

What does non correction in the 50:50 bmix blood test show?

Answer 15

Specific or non specific inhibitor OR
multiple factor deficiencies

Question 17

What does a correction of 50:50 mix tes suggest

Answer 17

Single factor deficiency as normal blood can provide the missing factor

Question 18

Causes of combined prolonged APTT and PT

Answer 18

Severe vit K deficiency
Advance liver disease
DOACs
Supratherapeutic warfarin therapy
Factor consumption eg DIC
Congenital common pathway factor deficiency, acquired inhibitors to common pathway factors

Question 19

What screening test can differentiate DIC, vit K deficiency/warafrin use and liver disease

Answer 19

Factor V, VII and VIII

Question 20

Why do mild vit K def and early stage liver disease only prolong PT

Answer 20

Factor VII has shorter half life than other factors - first one to be affected

Question 21

Why is DOAC monitoring unreliable

Answer 21

Prolonging of APTT and PT depends when checked, cant tell if tehrapuetic or not from levels

Question 22

How is APTT measured

Answer 22

Incubate citrated plasma with contact activator first

ADD phospholopid and calcium - time for clot formation in seconds

Question 23

What test for if low factor VIII

Answer 23

VWD screen

Question 24

What does a normal VWD screen suggest

Answer 24

Haemophilia A

Question 25

What does abnormal VWD screen suggest

Answer 25

Von willebrand disease

Question 26

What test do if corect 50/50 mi and normal factor levels

Answer 26

Long incubation APTT for early contact factor deficiency

Question 27

What time is not correcting for 50/50 mix

Answer 27

> 41 seconds

Question 28

If non correction 50/50 mix and then non specific inhibitor what test for

Answer 28

Antiphospholipid antibody testing

Question 29

What test do if consistent with inhibitor after non correction of 50/50 mix

Answer 29

Inhibitor assay for factor that is decreased

Question 30

50/50 mix how works

Answer 30

APTT reported within 5 minutes of the mix (“immediate”)
after 60 minutes incubation at 37°C -detect progressive inhibitor (this usually indicates a factor VIII inhibitor)

Question 31

What would find if factor VIII inhibitor on 50/50 mix

Answer 31

Progressive inhibitor after 60 mins incubation

Question 32

What causes signiicantly prolonged APTT (>100s) but no bleeding

Answer 32

Contact factor deficiency (prekallikeren, HMW kininogen)+factor XII

Question 33

What is INR

Answer 33

Standardised PT

Question 34

What is ISI

Answer 34

International Sensitivity Index (indicates sensitivity of reagent to deficiencies in Vitamin K dependent factors compared to the WHO reference standard)

Question 35

Prolonged PT tests to order after

Answer 35

Liver enzymes, albumin, bilirubin
50/50 mix for correction

Question 36

What suspect if correction of 50/50 in prolonged PT

Answer 36

Deficiencies

Question 37

What suspect if non-correction of 50/50 in prolonged PT

Answer 37

Specific or non sepcific inhibitors to Factor VII

Question 38

Differentials for prolonged APTT AND PT

Answer 38

• Thrombin inhibitors (heparin, direct thrombin inhibitors or direct Xa inhibitors)
• Vitamin K deficiency (including use of Vitamin K antagonists)
• DIC
• Liver disease
• Paraproteinemia
• Congenital factor II, V, X or fibrinogen deficiencies
• Fibrinogen depletion (hemodilution, massive hemorrhage, fibrinolysis)
• Dysfibrinogenemia (acquired vs congenital)
• Acquired factor X deficiency from amyloidosis
• Acquired factor V inhibitors topical bovine thrombin, postoperatively, post-cardiac bypass
• Any common pathway factor inhibitors

Question 39

Differentiating between factor V, factor VII and factor VIII

Answer 39

V - NOT vit K dependent, only made in liver, common
VII - Vit K dependent, only made by liver, exrinsic
VIII -NOT vit K dependent, Lliver and endothelial cells make, intrinsic

Question 40

Why can FVIII be elevated in disorders such as liver disease

Answer 40

Acute phase reactant