Fresh whole blood collected in
sodium citrate at a 9:1 ratio of blood to anticoagulant
Ca++ is bound by sodium citrate keeping blood from
clotting
Specimen centrifuged and plasma used
in testing
Plasma is mixed with reagent
containing:
Tested within 2 hours or stored at
-20oC for 2 – 5 days
Partial thromboplastin
(Phospholipid
substitute for PF3)
Incubation time of 3 minutes
Timer started with addition of Ca++ and stops when clot forms