Prothrombin time (PT) measures the blood's ability to clot properly. A prothrombin time test uses a control sample to establish a normal rate for how fast blood should clot. A patient's blood is compared to that sample, and abnormal results are stated as prolonged beyond control. This means how many seconds longer it took the patient's blood to clot than the sample. For example, let's say the normal range is 10 -13 seconds. If a patient's prothrombin time level was 3 seconds beyond control, that means it took 16 seconds for his/her blood to clot.

Click here for another, simpler explanation of prothrombin time.

Click here for information on normal prothrombin time values and what abnormal results may indicate.

Note: For the purposes of this project, we will consider prothrombin time in seconds, not in INR.

Prothrombin time is tested as part of a routine liver panel, which also includes:

• ALP
• AST
• ALT (To learn more about how ALT and AST results should be interpreted together, click here.)
• Serum Albumin
• Serum Globulin
• Serum Ammonia
• Serum Bilirubin

Possible causes include:

• Liver disease
• Cirrhosis
• Leptospirosis

Healthy Liver Function

Understanding the Liver