Partial Thromboplastin Time
Partial thromboplastin time (PTT) is a blood test that measures the time it takes your blood to clot.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
|Partial thromboplastin time (PTT):||
|Activated partial thromboplastin time (APTT):||
The heparin dose is changed so that the PTT or APTT result is about 1.5 to 2.5 times the normal value.Reference 1
- 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 be caused by bleeding disorders, such as Reference hemophilia Opens New Window or Reference von Willebrand's disease Opens New Window.
- A longer-than-normal PTT or APTT can be caused by liver disease, kidney disease (such as Reference nephrotic syndrome Opens New Window), 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 or lupus anticoagulant syndrome. These conditions happen when the immune system makes Reference antibodies Opens New Window 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. If you have a longer PTT, you may have a higher risk of bleeding.
|By:||Reference Healthwise Staff||Last Revised: Reference September 6, 2012|
|Medical Review:||Reference E. Gregory Thompson, MD - Internal Medicine
Reference Joseph O'Donnell, MD - Hematology, Oncology