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Partial Thromboplastin Time  The PTT should be 25 to 35 seconds. If the person is taking blood thinners, clotting takes longer 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 aPTT is 30-40 seconds. [1, 2, 3] 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  Interpretation A prolonged aPTT result m...