A partial thromboplastin time (PTT) is a simple blood test that times your blood’s ability to clot. It is used to test for bleeding problems or disorders, or to measure the levels and effectiveness of certain types of medicines—usually blood thinners such as heparin or warfarin. After a small amount of blood is collected from your arm, a laboratory specialist will add chemicals top the sample and time the clotting action.
The normal range for clotting in a healthy adult's blood taken as a partial thromboplastin time (PTT) is between 25 to 35 seconds (if you are taking blood thinners, this can take up to two and a half times longer), although your health care provider will tell you what your range should be.
A longer-than-normal PTT may signal low levels of clotting factors in the blood, characteristic of bleeding disorders such as hemophilia (a rare bleeding disorder that affects blood's ability to clot) or von Willebrand's disease (which effects the ability of platelets in the blood clump together).
A longer-than-normal PTT can also be indicative of low levels of certain medications--usually, blood thinners, such as heparin or warfarin (Coumadin). Your health care provider can advise you how to adjust your medication dosage back to therapeutic levels.
Complications due to lupus can also cause longer-than-normal PTT results such antiphospholipid antibody syndrome and lupus anticoagulant syndrome. Both these syndromes cause the immune system to attack clotting factors in the blood.
Acute Phase Reaction
Decreased PTT levels may also indicate an acute phase reaction, a temporary condition in which body tissues become inflamed due to injury and can repress clotting response times. Retesting usually shows a return to regular levels.
Another cause of longer-than-normal PTT levels can be liver disease, particularly cirrhosis (scars on the liver).