The patient is asked what medications they are on, to see if they may influence test results. If the patient is on heparin therapy, the blood sample is drawn one hour before the next dose of heparin.
Normal APTT results are usually between 25-40 seconds; PTT results are between 60-70 seconds. APTT results for a patient on heparin should be 1.5-2.5 times normal values.
Abnormal results are increased levels in those with a bleeding disorder or liver disease. With those taking heparin, low levels indicate the dose is too low, high levels indicate the dose is too high.