Blood Clotting Q&a

Bio Chemistry Blood Clotting Hemostatis Tests: PT & aPTT Questions & Answers

For Personal Study

1) Which are the Serine Proteases? Serine proteases: Factors VIIa, IXa, Xa, IIa (thrombin), XIa and XIIa 2) Which are the Vitamin K dependent clotting factors? Vitamin K-dependent clotting factors: VII, IX, X, II 3) Which are the Natural Anti-coagulants? Natural anti-coagulants • TFPI: VIIa and Xa inhibition • Activated Protein C (APC)/protein S: VIIIa and Va inhibition • AT-III and endogenous heparin: IXa, Xa and IIa inhibition 4) The Natural anti-coagulate TFPI causes the inhibition of what other factors? VIIa and Xa inhibition 5) The natural anti-coagulant Activated Protein C (APC)/protein S cause the inhibition of what other factors? VIIIa and Va inhibition 6) The natural anti-coagulant AT-III and endogenous heparin: cause the inhibition of what other factors? IXa, Xa and IIa inhibition 7) Warfarin is a what type of analog? vitamin K analog 8) Warfarin a (vitamin K analog): causes inappropriate post-translational modifications on which factors? VII, IX, X and II 9) Exogenous Heparin: binds what ? AT-III

10) After Exogenous Heparin: binds AT-III, which in turn, inhibits what other factors? IXa, Xa and IIa 11) What type of blood sample is needed for coagulation tests? PLASMA 12) Given tests results what can be predicted? predict possible pathology 13) Given pathology what can be predicted? predict test results 14) What is added as an anticoagulant in a plasma sample? Citrate 14A) Citrate is a what? calcium chelator (sequester)

15) A Bleeding Time Test evaluates what? platelet function and for von Willebrand factor diseases. 16) What is the Normal Value for a Bleeding Time Test? Normal values range from 1-9 minutes 17) Explain how a Bleeding Time Test is performed? It is a measure of the time it takes to stop the flow of blood from a standardized wound. • During the test a blood pressure cuff is placed below the elbow and inflated to 40 mmHg • A small, superficial cut (1 mm deep x 1 cm wide) is made in the forearm. • Blood is wicked away every 30 seconds. • Time is noted when bleeding stops. • Normal values range from 1-9 minutes. 18) From the test results provided, suggest a possible reason for the bleeding problem?

Platelet Count Decreased ; Bleeding Time Increased; aPTT Normal; PT Normal; Clot Solubility (Insoluble)? Thrombocytopenia

19) From the test results provided, suggest a possible reason for the bleeding problem? Platelet Count Normal ; Bleeding Time Increased; aPTT Increased to Normal; PT Normal; Clot Solubility (Insoluble)?

Von Willibrand Disease 20) From the test results provided, suggest a possible reason for the bleeding problem? Platelet Count Normal ; Bleeding Time Increased; aPTT Normal; PT Normal; Clot Solubility (Insoluble)?

Platelet Dysfunction or Aspirin Ingestion 21) A PT (prothrombin time) test evaluates what pathways? extrinsic pathway and common pathway

22) What 3 things does a PT Test require? Citrated plasma Thromboplastin Calcium

23) What is Thromboplastin derived from and what are the two important factors in it? from an animal brain extract that contains tissue factor III and phospholipids.

24) Due to the heterogeneous nature of thromboplastin preparations, PT values are calibrated using a reference preparation and are reported as what? international normalized ratio (INR).

25) Factor VII has the shortest half-life how long is it? (3 to 6 hours) and is the first to decline.

26) Why is PT the better test to use for monitoring warfarin therapy? Of the four vitamin K dependent clotting factors, Factor VII has the shortest half-life (3 to 6 hours) and is the first to decline. The PT test measures the extrinsic pathway and is very sensitive to a decrease in Factor VII. Warfarin is a vitamin K analog.

27) An aPTT test evaluates what pathways? intrinsic pathway and common pathway

28) What does an aPTT test require? Test requires the following: • Citrated plasma • Kaolin (a negatively-charged clay that provides “contact activation” of factor XII) • Phospholipids (usually phophatidyl serine) • Calcium

29) Do people with a deficiency in XII present any coagulation problems? No, XII is considered as a clotting factor because of its involvement in aPTT test.

30) Why is aPTT the better test to use for monitoring heparin therapy? Heparin binds to AT-III and activates it. An activated AT-III then inhibits IXa, Xa and thrombin. IXa is most sensitive to AT-III inhibition and is located in the intrinsic pathway. Thus, aPTT test is a better choice of coagulation test.

31) Patients with classic hemophilia commonly suffer from repeated hemarthrosis of ankles, knees and elbows. Why should a hemophiliac be warned not to use aspirin?

At joints, tissue factor is limiting. As a result, a person with hemophilia relies on platelet plug for hemostasis. For a person without hemophilia, when bleeding at joints, hemostasis is accomplished via an effective fibrin clot formation (primarily via intrinsic pathway and common pathway) and platelet plug formation.

32) Explain why individuals with severe liver disease or with vitamin K

deficiency tend to be susceptible to bruising. Vitamin K is required for the post-translational modifications of clotting factors VII, IX, X and II. This modification is crucial for a proper anchoring of activated clotting factors to “adhere” to the plasma membrane of activated platelets via calcium bridges. When vitamin K is deficient, the levels of properly modified clotting factors are reduced. When these four factors become activated, they are not able to associate with the activated platelets. Thus, coagulation is comprised, resulting in easy bruisability. 33) Why are newborn infants susceptible to hemorrhagic disease? Newborns are potentially vitamin K deficient, which make them susceptible to hemorrhagic disease. This tendency of being vitamin K deficient can be attributed to the following: 1. In utero, placenta is a poor conduit to hydrophobic substances, including fat-soluble vitamins. 2. At neonatal stage, many infants have immature liver, resulting in insufficient production of 8 clotting factors and inadequate modifications of the 4 vitamin Kdependent factors. 3. Breast milk is a poor source of vitamin K. (Formula contains 10X higher vitamin K compared to the breast milk). 4. Vitamin K, by nature, has a short half-life and is not stored in large quantities in the liver. 5. Sterile environment of the GI tract in infants also leads to a reduced production of vitamin K. In general, 50% of vitamin K is from dietary source, and 50% is made by intestinal flora. The flora will soon be established, ranging from 1 to 6 months.

34) What is the treatment for newborn infants deficient in vitamin K? Prophylactic treatment: vitamin K injection to newborns.

35) What is the therapeutic range of Warfarin?

Therapeutic range ~2.5X upper reference limit

36) What is the Therapeutic range of Heparin? Therapeutic range ~1.5-2.3 X upper reference limit

37) What might be a circumstance where a Bleeding Time Test is ordered? Occasionally, it is ordered before a surgery.

38) What clotting factors are not screened in a aPTT test? TF Ca2+ VII (7) XIII (13)

39) What clotting factors are not screened in a PT test? TF Ca2+ VIII, IX, XI, XII, XIII (8, 9, 11, 12, 13)

40) For the Following Patients propose a reason why they would have a bleeding problem? Patient Problem

Platelet Count

Bleeding

aPTT PT

Time

Clot

Possible

Solubility

Patient #1

N

N

▲

N

Insoluble

Patient #2

N

N

N

N

Sol

Deficiency of

XI, IX, VIII

Deficiency of XIII

Patient #3

N

N

N

▲

Insoluble

Patient #4

N

N

▲

▲

Insoluble

Deficiency of VII

Deficiency of X, V, II and I Liver Disease Vitamin K deficiency Heparin therapy and/or Warfarin therapy