TEST FOR PROTHROMBIN CONSUMPTION INDEX (PCI) (TEST TO MEASURE THE EXTRINSIC SYSTEM)

TEST FOR PROTHROMBIN CONSUMPTION INDEX (PCI) :-

This test measures the extrinsic pathway of coagulation.About 95% of prothrombin-is utilised by activation to thrombin when whole blood clots. Citrated plasma is clotted in the absence of platelets and much less prothrombin is consumed. Thus, by comparing the clotting time of serum and plasma in the presence of fibrinogen, the contribution of platelets to the coagulation process can be determined.

Specimens 

Collect 1.8 ml of blood in a tube containing 0.2 ml of 3.8% sodium citrate and 2.0 ml blood in a plain tube. Keep the plain tube at 37°C for one hour and centrifuge to separate the serum. Centrifuge the citrated blood as for prothrombin time (1000 g for 15 minutes). 

Reagents

1. Brain thromboplastin 

2. 0.025 M Calcium chloride 

3. Fibrinogen: Human fibrinogen, 150-200 mg in 100 ml saline. 

Technique 

(1) Add 0.1 ml of serum to two glass tubes and keep at 37°C.

(2) Add 0.1 ml of brain thromboplastin to one tube, start a stop watch.

(3) At the end of one minute, add 0.1 ml calcium chloride and mix.

(4) After two minutes, remove any fibrin formed with an applicator stick; and add 0.2 ml fibrinogen. Note the time required for clot formation at 37°C.

(5) Repeat the same procedure with the second tube, record average time.

(6) Repeat the same procedure with citrated plasma.

Calculation
 

Prothrombin Consumption Index = Plasma clotting time/Serum clotting time x 100

Normal range

 <30% Interpretation

PCI may be prolonged due to

1. Thrombocytopenia

2. Platelet coagulation defects

3. Platelet aggregation defects