Blood naturally clots to slow or stop bleeding. Sometimes, however, the blood might not clot, or certain chemicals in blood might indicate internal bleeding, or even liver problems. Prothrombin Time (PT) is a test a doctor might order to determine the rate at which the blood clots. These tests might prove crucial in understanding why the patient is bleeding, why blood might not be clotting, or might even help in the diagnostic stage
If a patient has had problems with blood clotting in the past, and takes medicine to facilitate clotting, or if the patient is taking blood thinners, PT tests might also help the doctor determine the efficacy of the medication. In these circumstances, the solution might be as simple as upping a dosage or switching medications altogether.
Taking the Test
Prothrombin time (PT) is determined by analyzing a blood sample, so a nurse or a technician will need to draw blood through a needle. These are relatively painless procedures and usually don’t require large samples.
Interpreting the Test
The rate of Prothrombin time is calculated by how long, in seconds, it takes for the blood to clot. The standard time for blood to naturally clot is usually approximately 11 to 13 ½ seconds. Results are typically calculated and presented using the International Normalized Ratio (INR). The average INR is typically between 0.8 and 1.1.
If, however, a patient is taking a medication designed to thin the blood, the clotting time may take as much as 2.0 or even 3.0 INR. These rates are normal on medicine such as Warfarin, so there’s no reason for these numbers to cause concern.
Understanding the Results
Since Prothrombin time (PT) is determined in seconds, it’s easy for medical professionals to conclude that blood is clotting too fast or too slowly, or if PT is average. Tracking the rate of PT will help a doctor diagnose potential causes. While chemicals that help the blood clot are manufactured in the liver, abnormal PT might indicate liver problems. In many cases, however, it might also indicate something less serious.
Too much or too little vitamin K intake may result in fast or slow PT, for example. Insufficient protein levels may also affect PT. Additionally, so can medications containing estrogen, such as birth control pills.