What is a PTT (partial thromboplastin time) test?A partial thromboplastin time (PTT) test measures the time it takes for a blood clot to form. Normally, when you get a cut or injury that causes bleeding, proteins in your blood called coagulation factors work together to form a blood clot. The clot stops you from losing too much blood.You have several coagulation factors in your blood. If any factors are missing or defective, it can take longer than normal for blood to clot. In some cases, this causes heavy, uncontrolled bleeding. A PTT test checks the function of specific coagulation factors. These include factors known as factor VIII, factor IX, factor X1, and factor XII.Other names: activated partial thromboplastin time, aPTT, intrinsic pathway coagulation factor profile
