: Thrombin Time

: What the Thrombin Time Measures

: When blood clots, thrombin converts a protein called fibrinogen into fibrin strands that form the clot. The thrombin time measures the speed of this specific step by adding a standard amount of thrombin to a plasma sample and timing how long the clot takes to form. A longer-than-expected time can point to problems with fibrinogen or to substances that interfere with this reaction.

: Why Your Doctor Might Order It

: Your doctor may order a thrombin time when you have unexplained bleeding or abnormal results on other clotting tests, such as the prothrombin time (PT) or activated partial thromboplastin time (aPTT). It is also used to detect or monitor certain blood thinners, such as heparin, and to help evaluate fibrinogen disorders or other conditions that affect clot formation.

: What Affects the Results

: Results can be influenced by the level and function of fibrinogen, the presence of heparin or related anticoagulant drugs, and substances called fibrin degradation products that appear when clots break down. Some inherited or acquired conditions affecting fibrinogen can also lengthen the clotting time. Your care team interprets the result alongside your history and other laboratory tests rather than in isolation.

: What the Test Involves

: The thrombin time is performed on a blood sample drawn from a vein, usually in your arm, and the plasma is separated for testing in the laboratory. It is a routine blood draw, and you should follow any instructions from your care team about medications or fasting. The result is reported as a clotting time, typically in seconds, that your doctor compares with the laboratory's expected range.