Prothrombin time test procedure: Principle, Requirements, Factors

Prothrombin time test procedure used to check the activity of the EXTRINSIC and COMMON coagulation pathways under standard conditions.

When thromboplastin (prepared from rabbit brain) and calcium are added to citrated plasma. It activates the coagulation pathway, resulting in a FIBRIN clot. The time taken, for this clot to form is called prothrombin time.

Prothrombin time test requirements

The following are the requirements for the prothrombin time test procedure.

1. Patient platelets have poor plasma
2. Normal control plasma
3. Thromboplastin
4. Test tube
5. Pipette
6. A water bath
7. Stopwatch
8. Table lamp

Prothrombin time test procedure

1. 1st set the lamp behind the water bath in such a way that the test tube can be seen against it.
2. Place the glass tube in a water bath to warm it at 37 centigrade.
3. Place 100 micro litter test plasma in one tube. After 1 minute add 200 microliter thromboplastin in it. Start the stopwatch instantly.
4. Examine the tube every 4 to 5 seconds for clot formation under the light by tilting.
5. Stop the watch, when a visible clot is formed.

Note: Repeat this procedure on patients’ plasma and note the clot-forming time.

9 factors affect the prothrombin time test

The following 9 factors affect the prothrombin time.

1. The deficiency of factors V, II , VII, and X increases the PT.
2. Heparin concentration increase PT.
3. Oral anti coagulant medicin.
4. Obstructive Jaundice.
5. Liver disease
6. Malabsorption
7. DIC
8. Vit- K deficiency
9. Hemorrhagic disease of the newborn

What is the normal value of the prothrombin time test?

PT’s normal value is 10 to 14 seconds.

Prothrombin time high

The following condition increases the PT.

1. The deficiency of factors V, II, VII, and X increases the Prothrombin time.
2. Vit- K deficiency
3. Liver disease
4. Heparin