Briefly explain how each of these tests is performed and the information that is gained from each:

a. Template bleeding time

b. Closure time

c. Aggregation tests: be sure to indicate the differential purposes of including: ADP, Collagen, Epinephrine

Answer:

The basic protocol for performing these tests are as given below:

A) PT test: In a PT test, blood sample is drawn and calcium is chelated from the sample by simply adding the blood to a tube of anti-coagulats (mainly containing oxalate or citrate ions) and plasma isolated. This blood of patients contains prothrombin. In order to convert this prothrombin to thrombin, some tissue factor (as an imitation of tissue injury) is added to the blood at normal human body temperatures. Subsequent addition of heavy salt such as CaCl₂ to the tube captures the anti-coagulant and blood starts clotting. This time gap between addition of salt and formation of a clot is measured and is called the PT time. The less is the PT time, the less isthe template bleeding time and more is the closure time.

B) aPTT test: In the aPTT test, blood is drawn in anti-coagulant containing tube the same way as in PT test, except that along with a heavy clacium salt, specialized activator is added to start specifically the intrinsic pathway of thrombus formation such as kaolins, cephalin etc. Additon of these substances bring about clot formation and the time gap between their addition and clot formation is calculated as aPTT time. Similar to PT test, the less is the PT time, the less isthe template bleeding time and more is the closure time.

Aggregation test: An aggregation test is used to analyse the efficacy of platelets to stick together in order to form a healthy clot during any injury. The entitites mentioned in the questions have following purposes in the test:

1. Collagen: Collagen is an inducer of platelet aggregation in vitro to perform a test.

2. ADP: It improves collagen adhesion in vitro to properly estimate collagen aggregation.

3. Epinephrine: It is a specific aggregation-starting factor which does not cause any physical change in shape of the platelets and mimics the proper in vivo condition in test tube as well.