Prothrombin time

Prothrombin time
Haematology
Coagulation
Rajesh B.K.
Nepal

1. Prothrombin Time (PT)

2. Name of the method: Quick’s method Specimen: Citrated plasma

3. Principle:- The prothrombin time is the time required for the plasma to clot after addition of tissue factor ( thromboplastin ) and an optimal concentration of calcium. This indicates overall efficiency of extrinsic pathway.

4. Requirements:- Water bath (37°C) Stop watch Test tubes Tissue thromboplastin 0.15 gm/dl Calcium chloride Platelets poor citrated plasma (PPCP) (mix 0.2 ml of 3.8% tri-sodium citrate with 1.8 ml of blood) prepared after centrifuging citrated blood at 3000 RPM for 15 minutes.

5. Procedure:- 1. Take 0.1 ml plasma in clean test tube. The plasma should be pre-warmed at 37°C in waterbath . 2. Add 0.1 ml tissue thromboplastin , mix well and incubate at 37°C for 2 minutes. 3. Add 0.1 ml calcium chloride solution, mix and start the stop watch. 4. At the first appearance of a fibrin clot, stop the watch immediately.

6. 5. Record the time. 6. Report prothrombin time in seconds.

7. Normal range:- 12-15 seconds

8. International normalized ratio (INR):- INR = (PT ratio)^ ISI of tissue thromboplastin used. Normal range of INR= 1.0-1.2 ISI = International sensitivity index. PT ratio= PT of test PT of control

9. Clicinal significance:- Prolonged PT is found in:- Oral anticoagulant therapy Vitamin K deficiency Liver disease Disseminated intravascular coagulation (DIC) Renal disease Deficiency of factors I, II, V, VII or X.

10. Sources of error:- Faulty collection of blood. Excess anticoagulant or insufficient anticoagulant. Reagent not good. Glass tubes are not clean. Incorrect temperature of water bath. If temperature is increased, factors may be destroyed.