Prothrombin
Time (PT) - 1
Specimen requirements:
Fresh whole blood collected in
sodium citrate at a 9:1 ratio of blood to anticoagulant
Principle:
Ca++ is bound by sodium citrate keeping blood from
clotting
Specimen centrifuged and plasma used
in testing
Plasma is mixed with reagent
containing:
Ca++
Tested within 2 hours or stored at
-20oC for 2 – 5 days
Tissue thromboplastin
(human or rabbit tissue)
Phospholipid substitute
for PF3
Timer starts with addition of
reagent and stops when fibrin monomer is detected