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: | Robin Parks, MS | Last Updated: September 15, 2008 |
| Medical Review: | Anne C. Poinier, MD - Internal Medicine Brian Leber, MDCM, FRCPC - Hematology | |
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| Topic Contents | |
| Test Overview | |
| Why It Is Done | |
| How To Prepare | |
| How It Is Done | |
| How It Feels | |
| Risks | |
 | Results |
| What Affects the Test | |
| What To Think About | |
| References | |
| Credits | |