VII. TEACHING POINTS

1. Inherited coagulopathies are not always recognized in childhood. They should be included in the differential diagnosis of any person with a bleeding disorder.



2. It is extremely important to obtain a complete history from patients with coagulation disorders.



• The family history should also be explored in detail. If positive, the family history is very helpful in establishing a diagnosis of an inherited bleeding disorder.
• A complete history of drugs and diet should also be obtained because both can alter hemostasis.



3. The clotting scheme is useful is assessing clotting factors in vitro.



• The activated partial thromboplastin time (aPTT) is prolonged by abnormalities of all the clotting factors with the exception of factor VII.
• The prothrombin time (PT) is prolonged by abnormalities of factors V, VII, X, prothrombin (factor II), and fibrinogen
• Factors II (prothrombin), VII, IX, and X are vitamin K dependent



4. The partial thromboplastin time (aPTT) and prothrombin time (PT) can be used to identify a specific clotting defect. Patients test results may include any of the following:



• both tests normal
• aPTT prolonged and PT normal
• PT prolonged and aPTT normal
• both tests abnormal



5. An analysis of the aPTT and PT results taken together helps to further delineate the nature of the coagulation defect, as shown in the following table.

Interpretation of PT and aPTT
PT Long / aPTT Nl.	PT Nl. / aPTT Long	PT Long / aPTT Long
Low factor VII Vitamin K deficiency Warfarin therapy Liver disease	Low factor VIII, IX, XI, or XII Lupus anticoagulant Heparin therapy Low prekallikrein (PK) or high molecular weight kininogen (HMWK)	Low factor V or X Low fibrinogen or prothrombin High hematocrit Vitamin K deficiency Warfarin therapy Liver disease
Adapted from Aggarwal & Alving, Blood Components, p5




6. von Willebrand factor (vWF) plays an important role in both platelet plug formation and coagulation.



• The higher molecular weight multimers mediate platelet adhesion to the endothelial matrix.
• vWF binds and stabilizes circulating factor VIII (which rapidly degrades in the absence of vWF).



7. The ELISA test can be used for quantitative analysis of von Willebrand factor. The Ristocetin cofactor test can be used for qualitative analysis of von Willebrand factor.



8. There are three major subtypes of von Willebrand disease. Type 1 is the most common and least severe.



9. It is important to identify the patient’s subtype of von Willebrand's disease in order to choose appropriate therapy.

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