Activated Partial Thromboplastin Time (aPTT) - 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:
Activator - kaolin
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