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.