Clinical
Utility of aPTT
Monitor effects of unfractionated
heparin therapy
Can’t be used to monitor
low-molecular weight heparin therapy (neutralizes factor Xa)
aPTT performed 4-6 hours following
start of heparin therapy
aPTT performed every 6 – 24 hours
during therapy
As a monitoring test:
aPTT continued for 5 days or until
oral anticoagulant
therapy is stabilized
As a
diagnostic test:
Run along with PT when hemorrhagic
disorder suspected or in recurrent thrombosis
Perform aPTT if lupus anticoagulant
suspected
Will be prolonged if single-factor
deficiencies is <50%
Will be prolonged if FDP or
paraproteins present