3. Haemostasis tests

Question 1

Bleeding time, bleeding mucosal time

Answer 1

NOT the test for coagulopathies.

Sharp sterile blade, 0,1-0,2 mm deep arms 0,5 cm long incision on the inner part of external ear or on the buccal mucosal surface. Wipe the blood UNDER the incision (not to remove thrombocyte-thrombus) in 20-30 sec interval. Measure the time from the appearance of the first drop of blood until the ceasing of the bleeding. BT is dependent on thrombocytes function, platelet count and capillary function
Normal BT 3-5 min

Question 2

Coagulation time (CT)

Answer 2

Fresh, not-coagulated blood, immediately after taking sample. Preferably from only one vein puncture to avoid increase of tissue factor (factor 3). Some drops of the blood are put on the glass and time til the appearance of first fibrin strands is measured. Normally they should appear within 1-2 minutes

Question 3

Coagulation time in ACT (activated clotting time) tube

Answer 3

Test tube containing SiO2 (commercially available tube, called ACT tube), put there some fresh blood, put it in the thermostate (37) and check the time of complete coagulation.

SiO2 activates Factor 12 (Hagemann factor), activated Factor 12 activates Factor 9 and kallikreinogen, kininogen (fibrinolytic pathway).

Normal time is 3 min

Question 4

Platelet (thrombocytic) count

Answer 4

1. Microscopical checking of the flood smear.
2. Using automated cell counter. Can be uncertain because calculation is done based on size of blood particles. Sometimes big platelets are counted as small RBCs and small RBCs as big platelets.

General platelet count is 200-800 x 10⁹/l

Question 5

What are major causes of thrombocytopenia

Answer 5

• decreased production in the bone marrow
• increased utilisation (DIC: disseminated intravascular coagulopathy)
• increased destruction (autoimmune thrombocytopenia)
• increased sequestration (splenomagaly)
• increased loss (chronic bleeding)

Question 6

Clot retraction test

Answer 6

If the blood clot is left in he tube for some hours, it will become smaller and serum will appear around the clot. The reason of retraction is platelet protein thrombostenin. Normally volume of released serum within the hour is approx 25% of the whole volume of the initial clot. If the clot retraction is slower or does not happen at all we can suspect thrombocytopathy

Question 7

Platelet aggregation test

Answer 7

This test can be performed when we suspect thrombocytopathy. Aggregometers will estimate the aggregating ability of platelets correctly. Device gives numerical values.

Question 8

Different sizes of thrombocytes in different species

Answer 8

• smallest (3-5 fl) - horses, cattle, sheep
• bigger (7-8 fl) - swine, dogs
• biggest (10-15) - cats

Question 9

Major causes of thrombocytopathies:

Answer 9

• improper development of platelets
• Von Willwbrand’s disease
• uraemia, liver failure, NSAIDs treatment, myelo- and lymphoproliferative diseases

Question 10

Prothrombin time (PT):

Answer 10

Gives information about the function of the extrinsic pathway because the coagulation cascade is triggered by adding tissue factor (and Ca++) to the decalcinated plasma sample.

Factors involved in PT are: 7, 10, 5, 2, 1, 13

Normal PT time is 10-15 sec

Question 11

Activated partial thromboplastin time (APTT):

Answer 11

Gives information about intrinsic pathway because the cascade is triggered by providing surface activation (imitating the effect of free collagen) and adding platelet factor 3 (PF3) and Ca++ for the activation of Factor 10

Normal time: 20-30 sec

Factors involved in APPT: 11, 9, 8, 10, 5, 2, 1, 13

Question 12

Thrombin test (TP):

Answer 12

Decalcinated plasma is mixed with just thrombin. In this case coagulation depends only on the concentration of fibrinogen and Factor 13 in the plasma.

Question 13

What test is used to check extrinsic coagulation pathway?

Answer 13

Prothrombin test

Question 14

What test is used to check intrinsic coagulation pathway?

Answer 14

Activated partial thromboplastin time

Question 15

Thrombin time (TT)

Answer 15

Decalcinated blood should be simply mixed with a reagent containing thrombin only. In this case coagulation time depends on the conc of fibrinogen and Factor 13 in the plasma.

Question 16

What is the role of vit K in coagulation?

Answer 16

Function of vit K is to exaggerate the post-synthetic gamma-carboxylation of Factors 7, 9, 10, 2 in the liver (vit K is the co-factor of the enzyme catalysing the attachment of a carboxylate group on the gamma C atom of the protein molecule after synthesis). This makes these factors being able to bind Ca++ and become functionally active

Question 17

Fibrin degradation time (FDT)

Answer 17

Fibrinolytic pathway is responsible for keeping the clot formation within normal limits. In the end of this pathway plasmin cleaves fibrin strands into small pieces. Before total degradation increased level of fibrinolysis products and fibrinogen breakdown products can be measured in the blood.

Very helpful for early diagnosis of DIC (disseminated intravascular coagulopathy)

Question 18

DIC (disseminated intravascular coagulopathy)

Answer 18

Common acute disorder, usually a secondary problem. In case of DIC microthrombus formatin and fibrinolysis are present at many different places of the body simultaneously.

Question 19

Von Willebrand disease

Answer 19

Von Willebrand factor (or complete Factor 8) is deficient. Increased BT, dedcreased clot retraction ability and sometime coagulation disorders too

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