Hematology

CHAPTER 2
Hematology

Christine Du

Test Taking Tip

Hematology requires lots of memorization. Important topics to look over include bleeding disorders and anticoagulants. These are basic questions you don’t want to miss.

THE COAGULATION PATHWAY

Sequence of the intrinsic pathway of coagulation:

Prekallikrein + HMW kininogen + Factor XII + exposed collagen → activates Factor XI → activates Factor IX, combines with Factor VIII → activates Factor X, combines with Factor V → converts prothrombin (Factor II) into thrombin. Thrombin converts fibrinogen into fibrin.

FIGURE 2-1. Schematic of the coagulation system. HMW, high molecular weight. (Reproduced from Brunicardi FC, Andersen DK, Billiar TR, et al. Schwartz’s Principles of Surgery. 9th ed. http://www.accessmedicine.com. Copyright © The McGraw-Hill Companies, Inc. All rights reserved.)

Sequence of the extrinsic pathway of coagulation:

Factor VII + tissue factor → activates Factor X, combines with Factor V → converts prothrombin into thrombin. Thrombin converts fibrinogen into fibrin.

Which factor is the convergence point and common to both the extrinsic and intrinsic pathways of coagulation?

Factor X

What does the prothrombin complex consist of?

Factor V, X, platelet factor 3, and prothrombin catalyzes the formation of thrombin

What function does thrombin have?

Activates factors V and VIII, activates platelets, and converts fibrinogen into fibrin and fibrin split products. It is instrumental in coagulation

Which factor has the shortest half-life?

Factor VII

What factor can be used to differentiate a consumptive coagulopathy from hepatocellular disease?

Factor VIII:C; consumptive coagulopathy will have reduced levels of all factors and hepatocellular disease will have reduced levels of all factors except factor VIII

Which factors are known as the labile factors (activity lost in stored blood)?

Factors V and VIII

What function does factor XIII have?

Cross-links fibrin

What does protein C do?

Degrades fibrinogen and Factors V and VIII (vitamin K dependent)

What does protein S do?

Acts as protein C cofactor (vitamin K dependent)

What does Von Willebrand factor (vWF) do?

Links collagen to the GpIb receptor on platelets

What is the function of antithrombin III?

Binds heparin, inhibits Factors IX, X, XI, and thrombin

Where does tissue plasminogen activator come from and what does it do?

Released from endothelium and it converts plasminogen into plasmin

What does plasmin do?

Degrades fibrinogen, fibrin, and Factors V and VIII

What is the natural inhibitor of plasmin called and where does it come from?

Alpha-2 antiplasmin; comes from the endothelium

What are the vitamin K–dependent factors?

Factors II, VII, IX, and X and proteins C and S

What function does tissue factor pathway inhibitor have?

Inhibits factor X

LABORATORY TESTS AND DATA

PT measures the function of these factors:

Factors II, V, VII, and X and fibrinogen

What 2 factors are not measured by the PTT?

Factors VII and XIII

PTT measures the function of these factors:

Factors II, V, VIII, IX, X, XI, and XII and fibrinogen

What is the normal value for bleeding time and what does it imply?

Normal bleeding time ranges from 3 to 9 minutes and implies platelet counts >50,000/mL and normal platelet function

What test aids in detecting circulating anticoagulants, qualitative abnormalities of fibrin, inhibition of fibrin polymerization, and measures the clotting time of plasma?

Thrombin time

Patients bleeding after a large number of blood transfusions should be considered to have:

Dilutional thrombocytopenia (vs hemolytic transfusion reaction)

What factors are common to both the PT and PTT?

Factors II, V, and X and fibrinogen