Secondary Hemostasis and Related Disorders Flashcards
What is the purpose of secondary hemostasis?
To stabilize the weak platelet plug via the coagulation cascade
Describe the process by which the platelet plug is stabilized.
Secondary hemostasis. Thrombin (factor II) converts fibrinogen into fibrin which is then cross-linked to form stable platelet-fibrin thrombus.
Factors activating coagulation cascade
1) Activating substances - Tissue thromboplastin activates FVII (extrinsic pathway); Subendothelial collagen activates FXII (intrinsic pathway)
2) Phospholipid surface of platelets
3) Calcium (from platelet dense granules)
What does Prothrombin time measure?
Measures the extrinsic coagulation pathway (FVII) and common factors (FII, FV, FX and fibrinogen)
What does Partial Thromboplastin time measure?
Measures the intrinsic (FXII, FXI, FIX, FVIII) and common (FII, FV, FX and fibrinogen) pathways of the coagulation cascade
What activates factor VII?
Tissue thromboplastin (TT)
What activates factor XII?
Subendothelial collagen (SEC)
What is Hemophilia A? How is it acquired? What are the clinical presentations? What information does lab testing reveal? What is the treatment?
Deficiency in factor VIII. Predominantly X-linked but de novo mutations can occur. Presents with deep tissue, joint, and postsurgical bleeding but depends on severity. Lab findings: Raised PTT, normal PT, depressed FVIII, Normal platelet count and bleeding time. Tx: Recombinant FVIII.
What is Hemophilia B? What is another name for Hemophilia B? How is it acquired? What are the clinical presentations? What information does lab testing reveal? What is the treatment?
Resembles Hemophilia A except FIX deficiency instead of FVIII deficiency. Also known as Christmas disease. Predominantly X linked but de novo mutations can occur. Presents with deep tissue, joint, and postsurgical bleeding; Severity depends on deficiency. Lab findings: Raised PTT, normal PT, depressed FIX, Normal platelet count and bleeding time. Tx: Recombinant FIX
Describe the condition of coagulation factor inhibition. Which antifactor-Ab is most common?
Acquired Ab against a coagulation factor. Anti-FVIII Ab is most common.
Using laboratory tests, how would you determine whether somebody has Hemophilia A or they have a coagulation factor inhibitor.
If you transfuse a patient with FVIII and their PTT time falls, the person has Hemophilia A. If the patient has a coagulation factor inhibition condition, the PTT will remain persistently high.
Describe Von Willebrand disease. Describe the genetic inheritance and the most common presentation. Describe lab findings. What is treatment for vWF disease?
Most common inherited coagulation disorder and can be either a qualitative or quantitative (commonly autosomal dominant with decreased vWF levels). Presents with mild mucosal and skin bleeding. Increased bleeding time, increased PTT - FVIII has a shorter half-life b/c vWF is normally a stabilizer, normal PT, Abnormal ristocetin test; Tx: Desmopressin which increases vWF release
How does the ristocetin test work and what is it used to diagnose?
Ristocetin induces platelet agglutination by causing vWF to bind to GPIb. Lack of vWF results in lack of agglutination which results in an abnormal test. Test used to Dx von Willebrand Disease.
Describe the mechanisms of activation and by which Vitamin K works in the coagulation cascade
Vit K is activated by epoxide reductase in the liver and gamma carboxylates (activates) FII, VII, IX, X, proteins C and S
3 ways which Vit K deficiency occurs
1) Newborns lacking Vit K synthesizing flora 2) Long-term AB Tx disrupts gut Vit K synthesizing gut flora 3) Malabsorption
