Reasons you may not be able to
have the test or why the results may not be helpful include:
Taking medicines that can affect the action of
blood thinners (such as warfarin) and vitamin K. These include antibiotics,
aspirin, cimetidine (Tagamet), barbiturates, birth control pills,
hormone replacement therapy (HRT), and vitamin K
Having severe diarrhea or vomiting that causes fluid
loss and dehydration. This may make the PT time longer. If diarrhea is caused
by poor absorption of nutrients, vitamins, and minerals from the intestinal
tract (malabsorption syndrome), the PT may be longer because of a lack of
Eating foods that have vitamin K, such as beef liver,
pork liver, green tea, broccoli, chickpeas, kale, turnip greens, and soybean
Drinking a lot of alcohol.
Taking some herbal products or natural remedies.
What To Think About
The U.S. Food and Drug Administration (FDA) has
approved a home test for prothrombin time (PT). If you need a PT test frequently and for a long time, you may want to ask your doctor if this home test is an option for you.
A PT is done at the same time of day
each time so test results can check whether the right dose of medicine is being
used to prevent blood clots.
Another blood clotting test, called
partial thromboplastin time (PTT), measures other clotting factors. Partial
thromboplastin time and prothrombin time are often done at the same time to
check for bleeding problems. For more information, see the topic
Partial Thromboplastin Time.