Haemostasis

Question 1

Define haemostasis.

Answer 1

Maintenance of vascular integrity and blood fluidity.Involves:

• Blood vessel endothelium
• Platelets
• Coagulation cascade - Ca2+, coagulation factors, fibrinogen
• Fibrinolytic mechanisms

Question 2

Outline primary haemostasis.

Answer 2

Formation of the platelet plug

• Vascular endothelial damage
• Exposed subendothelial collagen damage
• vWf binds collagen and platelets
• Platelets activated, attracted and loosely aggregated
• Local vasoconstriction (transient)

Question 3

Outline secondary haemostasis.

Answer 3

Formation of the definitive clot

• Exposure of subendothelial structures and platelet activation initiate thrombin generation
• Activation of the coagulation cascade
• Irreversible platelet aggregation
• Fibrin clot forms - fibrinogen to insoluble fibrin
• Fibrin forms a mesh via cross-linking

Question 4

Describe the clotting cascade.

Answer 4

Instrinsic - activated by contact with collagen (sustaining)Extrinsic - activated by tissue factor, extravascular(initiation)

Question 5

Outline tertiary haemostasis.

Answer 5

Fibrinolytic pathway.

• Lysis of platelet-fibrin network Plasmin mediated
• Activated plasminogen
• Balanced by inhibitors
• Fibrin degraded to FDPs (D-dimers)
• Vascular endothelium repair

Question 6

Which screening assays are used to assess the common and intrinsic pathways?Describe them

Answer 6

• ACT - Activated coagulation time - whole blood, platelets and calcium
• APTT - Activated partial prothrombin time

Question 7

Which screening assay(s) are used to assess the extrinsic and common pathways?

Answer 7

PT - prothrombin time

Question 8

Which screening assay(s) are used to assess the common pathway?

Answer 8

Thrombin clot time - prolonged suggests deficient or abnormal fibrinogen

Question 9

What clinical signs would be associated with a disorder of primary haemostasis?

Answer 9

• Oozing from small wounds
• Petechial and ecchymotic haemorrhage
• Mucous membrane bleeds - epistaxis and melaena
• Underlying disease signs

Question 10

Name some differentials for thrombocytopenia.

Answer 10

• Immune-mediated - primary and secondary
• Neoplasia
• DIC
• Infectious disease
• Breed related - CKCS, grey hound, shiba inu

Question 11

IMTP is associated with which agents/ conditions?

Answer 11

• Evan’s syndrome - IMHA
• Drug reactions - Abs
• Neoplasia
• Viral - FeLV
• Ehrlichia
• Vaccination

Question 12

What clinical signs are associated with IMTP?

Answer 12

• Petechia - ecchymotic haemorrhage
• Bruising
• Epistaxis, melaena
• Haematuria
• Hyphaema - eye
• Splenomegaly
• +/- pyrexia/ pallor

Question 13

At which platelet counts would a dog/cat be at risk of spontaneous haemorrhage?

Answer 13

• Dog

* Cat

Question 14

If you are investigating thrombocytopenia what platelet featurewould you make sure to check on a blood smear?

Answer 14

Platelet clumps - an automated blood count may miss this.

Question 15

What treatment can be used for animals with IMTP?

Answer 15

Immunosuppresives - reducing dose

• Corticosteroids/ cyclosporin/ azathioprine
• Vincristine
• Blood transfusion - platelet rich plasma/ whole blood - need to control IMTP w/ others
• Splenectomy

Question 16

In which clinical situations may you see reduced platelet function?

Answer 16

Excessive bleeding despite normal clotting profile.

• Azotaemia
• vWb disease
• Hyperproteinaemia
• BM disease
• hepatic disease
• Drug therapy - NSAIDs
• DIC

Question 17

Which screening assay(s) is used to assess platelet function?

Answer 17

• BMBT - Buccal mucosal bleeding time

* Clot retraction - crude (affected by thrombocytopenia)

Question 18

von Willebrand factor is vital for which stage of blood clotting?

Answer 18

Platlet adherence

Question 19

Describe the three types of vW disease.

Answer 19

1 - most common, autosomal recessive, partial quantitative

• Mucosal bleeding and bruising
• Excessive haemorrhage in surgery
• 2 - qualitative
• 3 - severe quantitative

Question 20

Outline four tests which are used for diagnosis of vW disease.

Answer 20

• BMBT increased Antigenic test
• Remember citrated plasma for test
• vWf function assays - type 2
• Genetic testing - AHT

Question 21

What treatment could be used for vW disease?

Answer 21

• Cryoprecipitate - factor 8, fibrinogen , vWf multimers
• Whole blood/ citrated plasma
• DDAVP - t1 - increases vWf release

Question 22

• Normal platelet count
• Prolonded APTT
• Normal PT
• Normal FDPs
  A pattern like this would suggest a problem in which pathway?

Answer 22

Intrinsic secondary

Question 23

• Normal platelet count
• Normal APTT
• Prolonged PT
• Normal FDPs
  A pattern like this would suggest problems in which pathway.

Answer 23

Extrinsic

Question 24

Which clotting factors are affected by vitamin K antagonists such as Warfarin?Which has the shortest half-life?

Answer 24

2, 7, 9, 107 - less than 5 hrs (acute decrease in production)

Question 25

* Normal platelets * Prolonged PT and APTT  * Normal FDPs A pattern like this would suggest problems with which clotting pathway?

Answer 25

Intrinsic and extrinsic pathwaysX, V, II

Question 26

A consumption of a vit K antagonist would be suggested by what change in screening assays over time?Why?

Answer 26

* First prolonged PT * Then prolonged PT and APTT Since factor 7 has the shortest half life the extrinsic pathway is affected first.

Question 27

Breakdown of cross linked fibrin is characterised is characterised by an increase in which substance?

Answer 27

D-dimers

Question 28

Hypercoagulable states are associated with which conditions?

Answer 28

* IMHA * Pancreatitis * Nephrotic syndrome - antithrombin lost in urine * Hyperadrenocorticism * DM * Cardiac disease

Question 29

Which tests allows you to rule out a defect of primary haemostasis? * PLT count * BMBT * vWf genetic test * Clotting time * Clot retraction

Answer 29

BMBT

Question 30

Predict bone marrow findings in a case of IMTP. * Increased thrombopoiesis * Decreased thrombopoiesis * No change * Generalised hypoplasia

Answer 30

Increased thrombopoiesis

Question 31

All of the following can cause increased thrombopoiesis except.. * Hypoxia * Decreased PLT cound * Inflammation * Iron deficiency * Increased PLT loss

Answer 31

Hypoxia

Question 32

Which inherited coagulation defect causes prolonged PT without prolonged APTT? * Hereditary 11 deficiency * Hereditary thrombin (2) deficiency * Hereditary 7 deficiency * Hereditary 12 deficiency

Answer 32

Hereditary 7 deficiency

Question 33

What is the other name for an inherited deficiency of factor 8? * Haemophilia A * Hereditary thrombin deficiency * Haemophilia B  * Hereditary afibrinogenemia

Answer 33

Haemophilia A

Question 34

What factors are affected by rodenticide poisoning? * 2, 3, 4, 5 * 4, 7, 8, 9 * 2, 7, 9, 10 * 1, 5, 8, 13

Answer 34

2, 7, 9, 10Vitamin K dependent factors

Question 35

``` Which type of erythrocyte abnormality is often seen in animals with DIC? * Spherocyte * Schistocyte * Target cell - codocyte * Elliptocyte   ```

Answer 35

Schistocyte