Partial Thromboplastin Time

Activated Partial Thromboplastin Time, APTT (Activated Parital Thromboplastin Time), PTT (Partial Thromboplastin Time)

Results

Partial thromboplastin time (PTT) is a blood test that measures the time it takes your blood to clot. Normal values may vary from lab to lab.

Normal

Partial thromboplastin time

Partial thromboplastin time (PTT):	60–70 seconds
Activated partial thromboplastin time (APTT):	30–40 seconds

The heparin dose is changed so that the PTT or APTT result is about 1.5 to 2.5 times the normal value.

Abnormal values

• A longer-than-normal PTT or APTT can mean a lack of or low level of one of the blood clotting factors or another substance needed to clot blood. This can cause bleeding disorders, such as hemophilia or von Willebrand's disease.
• A longer-than-normal PTT or APTT can be caused by liver disease, kidney disease (such as nephrotic syndrome), or treatment with blood thinners, such as heparin or warfarin (Coumadin).
• A longer-than-normal PTT may be caused by conditions such as antiphospholipid antibody syndrome and lupus anticoagulant syndrome that cause clotting problems. These syndromes are a complication of lupus in which the immune system makes antibodies that attack blood clotting factors. This can cause the blood to clot easily in veins and arteries.
• The PTT can get longer when you are using heparin, so your PTT value needs to be closely checked.

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Author:	Jan Nissl, RN, BS	Last Updated September 25, 2006
Medical Review:	Patrice Burgess, MD - Family Medicine Joseph O'Donnell, MD - Hematology
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