Activated Partial Thromboplastin Time (APTT)
Joe Hing Kwok Chu
This test is a modification of the Partial
Thromboplastin Time (PTT). PTT does not contain added contact
activator and is relatively insensitive to the effect of heparin.
APTT (activated partial thromboplastin time) is
where PTT adds a contact activator to its reagent, thus activating factor
XII (contact factor), and shortening the clotting time.
The APTT test is sensitive to heparin and evaluates
all the clotting factors except factors VII and factor XIII.
Reference Range of Test: A fibrin clot forms 2.5 to
3.8 seconds after the reagent is added to the specimen.