Prothrombine time (PT):
Preparation :1. 200 µ sodium citrate (0.2 ml) + 1.8 blood , mix well then centrifuge.
2. Prepare water bath at 37 º C .
3. Prepare 200 µ prothrombine reagent (Diaplastin) and put in water bath for 15 min and before ending by 3 minutes put the sample with it in the same path.
4. Put 100 µ plasma in test tube and put in water bath at the 12 min exactly of the reagent tube time then leave for 3 min.
5. Reset a stop watch, pour the reagent in the plasma tube with starting stop watch.
6. Mix in spherical direction till the first coagulation (increasing in viscosity) appears.
7. Record the time (PT) then from table of prothrombine get prothrombine activity & ratio and INR.