Chapter 2: Hemostasis and Coagulation

Question 1

What is primary and secondary hemostasis characterized by?

Answer 1

• Primary hemostasis is characterized by vasospasm and platelet plug formation (including; adhesion, activation, aggregation and cross-linking).
• Secondary hemostasis is characterized by activation of serial clotting factors via three cell-based steps (initiation, amplification and propagation).

Question 2

What are the normal and abnormal bleeding times?

Answer 2

Bleeding times between 2 and 10 minutes are considered normal. Times between 10 and 15 minutes are considered abnormal and associated with low-to-moderate risk for bleeding, while greater than 15 minutes is serious risk for spontaneous bleeding and severe platelet dysfunction or thrombocytopenia.

Question 3

What does the PT time measure? What can we use to standardize values of PT time accross institutions? what is the normal INR

Answer 3

PT time is a measure of the extrinsic and common pathways of coagulation cascade. Accordingly, PT measures the function of factors I (fibrinogen), II, V, VII and X. Because the PT can vary from laboratory to laboratory due to variations in reagents and detectors, the international normalized ratio (INR) was developed to standardized values across institutions independent of methods. A normal INR is 1.0. Prolongation in PT/INR usually occurs when factor levels fall below 30% to 50% normal range.

Question 4

What does the aPTT time measure?

Answer 4

The aPTT is a measure of the ex vivo intrinsic coagulation cascade compromising high molecular weight kininogen, prekallikrein, and factors I,II, V, IX, X and XI. Factor levels less than 30% of normal are usually required to affect aPTT.

Question 5

What is thromboelastography?

Answer 5

Rotational thromboelastography (TEG) is a viscoelastic hemostatic assay that measures whole-blood coagulation kinetics and biomechanical properties