How Blood Clots

Question 1

Primary hemostasis consists of formation of…

Answer 1

a platelet plug

Question 2

Secondary hemostasis consists of formation of…

Answer 2

fibrin mesh securing the platelet plug
- thrombin cleavage
- enzyme complex formation

Question 3

What triggers primary hemostasis or clotting

Answer 3

endothelial damage

Question 4

What is the role of platelets in primary hemostasis

Answer 4

• formation of a platelet plug
• provides a surface for the coagulation cascade to occur

(adhesion, aggregation, secretion of granular contents)

Question 5

Where are von willebrand factors made and stored

Answer 5

• made in endothelial cells and megakaryocytes
• stored in endothelial proteins & platelet granules

Question 6

Describe how von willebrand factor works

Answer 6

• exposed with endothelial damage
• sticks and unfolds to endothelium
• grabs platelets for plug formation

Question 7

What are the two main activators of platelets

Answer 7

collagen & thrombin

Question 8

What is the result of the final common pathway of the coagulation cascade

Answer 8

formation of an insoluble fibrin clot

Question 9

What is measured with the prothrombin time lab (PT)

Answer 9

the extrinsic pathway of the coagulation cascade

Question 10

What is measured with the partial thromboplastin time lab (PTT)

Answer 10

the intrinsic pathway of the clotting cascade

Question 11

What is thrombin responsible for

Answer 11

• cleaving fibrinogen resulting in an insoluble fibrin
• activation of platelets & coag factors
• activates regulatory pathways to shut off the coag cascade

Question 12

What lab tests help determine if there is a primary or secondary hemostasis problem

Answer 12

• primary: platelet number and function
• secondary: coag factor tests

Question 13

List 4 tests that assess platelet function

Answer 13

• platelet function analyzer (PFA-100)
• platelet aggregometry gold standard
• electron microscopy
• flow cytometry

Question 14

List 3 lab tests that assess coagulation factors

Answer 14

• thrombin time (TT)
• prothrombin time (PT) + INR
• partial thromboplastin time (PTT)

Question 15

What things prolong thrombin time (TT)?

Answer 15

• not enough fibrinogen
• dysfunctional fibrinogen (inherited or acquired - liver disease)

Question 16

What things prolong PT/INR?

Answer 16

• clotting factor deficiency (Factor II, V, VII, X)
• prolonged TT (fibrinogen issues)
• antiphospholipid Abs (lupus anticoags)

Question 17

What causes an acquired deficiency of factors VII, X, and II

Answer 17

• lack of vit K

Question 18

What causes an acquired deficiency of factor V

Answer 18

liver disease

Question 19

What can cause a prolonged PTT

Answer 19

• factor deficiency of XII, XI, IX, VII (hemophilia A & B)
• anything that prolongs TT or PT
• Antiphospholipid Abs

Question 20

What does the international normalized ratio (INR) measure

Answer 20

• based on PT
• designed to measure warfarin effect

Question 21

What lab tests should be used to assess for a suspected bleeding disorder

Answer 21

INR and PTT with assessment of platelets

Question 22

Which tests monitor heparin and warfarin

Answer 22

• heparin: PTT
• warfarin: PT/INR

Question 23

What can mixing studies assess when testing the coagulation cascade

Answer 23

• assesses if a prolonged clotting time is due to a factor deficiency or some sort of inhibitor
• only need 50% of each clotting factor for PT and PTT to be normal
• patient plasma mixed with normal plasma should bring deficient factor levels up and correct the clotting time
• if its an inhibitor/Ab problem the clotting time will still be prolonged