Reference Range
Partial thromboplastin time (PTT) and activated partial thromboplastin time (aPTT) are used to test for the same functions; however, in aPTT, an activator is added that speeds up the clotting time and results in a narrower reference range. The aPTT is considered a more sensitive version of the PTT and is used to monitor the patient’s response to heparin therapy.
The reference range of the aPTT is 30-40 seconds.
The reference range of the PTT is 60-70 seconds.
In patients receiving anticoagulant therapy, the reference range is 1.5-2.5 times the control value in seconds.
Critical values that should prompt a clinical alert are as follows:
aPTT: More than 70 seconds (signifies spontaneous bleeding)
PTT: More than 100 seconds (signifies spontaneous bleeding)