Thrombophilia Diagnosis Wk 3

Question 1

What is thrombophilia

Answer 1

A predisposition to form clots inappropriately

Question 2

Virchow’s triad

Answer 2

Arterial thrombosis (stroke/MI)
Alterations to normal blood flow
Injuries to the vascular endothelial Alterations to the constitution of the blood e. (hypercoagulability)

Venous thrombosis (DVT/PE)

Question 3

Constant balance consists on these three factors

Answer 3

Acquired x environmental x inherited
Between coagulation and anticoagulation

Question 4

Acquired factors (cell based)

Answer 4

• Cancer (neoplasm induced coagulation activation )
  • myeloproliferative (white cell) disorders - cell surface tissue factors expression
  • polycythaemia (red cell) - blood flow alteration
  • thrombocytosis (platelets) - blood flow alteration + activation surface
  • increase thrombotic risk X7
• heart failure
• recent MI/stroke

Question 5

Polycythaemia

Answer 5

Red cell

Question 6

Myeloproliferative

Answer 6

White cell disorders

Question 7

Thrombocytosis

Answer 7

Platelets

Question 8

Acquired factors (plasma based)
-Hyper-homocysteinaemia
Amino acid
Cysteine homologue
Biosynthesis intermediary

Answer 8

Impaired breakdown
(Homocysteine  Cystathionine)

Impaired remethylation (recycle)
(Homocysteine  Methionine)

Can be acquired or inherited
(often dietry, B6,B12, Folic acid)
(MTHFR gene polymorph C677T and A1298C)

1969 McCully  Atherscelerosis / Arterial thrombosis
Endothelial cell damage

1996 Den Heijer  x4 risk of Thrombosis

Mild Hyperhomocysteinaemia  5 to 7 % population

Question 9

Antiphospholipid syndrome (APS)
Alterations to the constitution of the blood (hypercoagulability)

Answer 9

^ auto-antibodies directed to platelet components required for coagulation pathway
• Cell membrane component Phosphatidylserine
• Cell protein component b2-GPI
• Primary or secondary to other auto-immune
(ie Rheumatoid/SLE)
• Ability to cause arterial and venous thrombosis
• Recurrent pregnancy loss
• Mostly acquired, can be inherited

Question 10

Lifestyle / environmental

Answer 10

• Pregnancy
• combined oral contraceptive pill
• hormone replacement therapy
• obesity (bmi>30=2x risk)
• trauma / immobility
• surgery

Question 11

Hereditary - raised levels of procuagulants

Question 12

Which to measure

Question 13

Hereditary reduced clearance

Question 14

Hereditary - inherited deficiency of natural anticoagulants

Answer 14

Direct inhibition - direct binding
Negative feedback loops - via the action of others
Anticoagulant or procoagulant
Thrombin → powerful procoagulant enzyme
powerful initiator of anticoagulation

Question 15

How to measure - quantitative, actual amount - monoclonal Ab. To specific factors

Answer 15

• Microtitre plate assays(ELISA)
• attached to latex beads
• electrophoresis - how much present

Question 16

Measure - qualitative

Answer 16

• Assay requires protein/protease to function
  • clotting assays (invoke pathway top to bottom)
  • chromogenic assays (functioning protein causes cleavage/colour change of chromogenic substrate)
  Doesn’t need standardisation

Question 17

Intrinsic pathway

Answer 17

Common pathway

Question 18

Antithrombin

Answer 18

• Serine protease inhibitor SERPIN
  -Inactivation of thrombin by 1:1 binding of active site serine
• increased activity in presence of heparin like substances:
• Dermatan sulphate from the endothelial
• Therapeutic heparin
  Deficiencies Type I Quantitative (Immunological)
  Type II Qualitative (Functional)

Question 19

Antithrombin (1965, Egeberg et al.)

Answer 19

• Autosomal dominant affected = 40 - 60% of normal levels
• 70% clot before age 50
• 1995 Tait et al. 10,000 blood donors

Question 20

Intrinsic pathway

Answer 20

Common pathway

Question 21

Protein C

Answer 21

Vitamin k dependent glycoprotein
- synthesized in the liver
- converted to activated protein C ( APC) by thrombin/ thrombomodulin cleavage
- requires co-factor protein S for full function
- Inactivates FVIIIa and FVa by cleavage at specific sites
- autosomal dominant inheritance

Question 22

Deficiency of protein C
-Less severe than antithrombin deficiency.

Answer 22

Type I. (Quantitative) more common than Type II. (Qualitative)

0.2-0.3% prevalence in normal population (Tait et al. 1995)

3% of all first time clots (DVT/PE)

10-15x more likely to have clot (DVT/PE)

Question 23

Protein S

Answer 23

Co-factor to Protein C
65% bound to C4b-Binding protein (inactive)
35% unbound (active component)

Type I. def (Quantitative FPS)
Type II. def (Qualitative FPS)
? Type III. def (Low FPS, Normal Total PS)

Question 24

Protein S

Answer 24

More difficult to measure
Lower in Women than Men
Decreased during pregnancy and Oestrogen therapies (HRT/COCP)

Prevalance ? 3% of all first time clots (DVT/PE )

? 1-2% of normal population

Limited risk factor ? x2
Differing effects depending on mutation/family

? Interactions with other factors

Question 25

Limited explanation of risk of thrombosis (10%)

(1993, Dahlback et al.) Resistance to Activated Protein C (APC) in approx 50% of patients presenting with unexplained thrombosis

Question 26

Natural anticoagulation negative feedback loop

Question 27

Factor FV Leiden

Answer 27

Single point mutation in FV

Factor V 1691 GA (Bertina, 1994)

Protects Factor V from degradation by APC

Autosomal dominant

Heterozygotes 3-8x risk of thrombosis
Homozygotes 80x risk of thrombosis

3-15% of normal population have mutation (asymptomatic)

Question 28

Prothrombin G20210A

Answer 28

Mutation causes raised level of prothrombin FII _ hyperprothrombinaemia

Increase Thrombin generation
2% of normal population (het)
6% of those with thrombosis (Poort et al. 1996)

Risk x0-3 (mild)

Cumulative risk ?
+ COCP = x15 risk of clot

Question 29

Inherited Thrombophilia

Answer 29

Antithrombin def 1 in 3,000
Protein C def 1 in 300
Protein S def 1 in 300
Factor V Leiden mutation 1 in 20
Prothrombin G20210A mutation 1 in 50-100

Question 30

Who do you measure?

Answer 30

Personal, family history of DVT/PE
Risk factors
<50

Question 31

Is testing worthwhile?