Blood clotting test
coagulation test · clotting test · INR · PT and PTT
A blood test that shows how fast your blood clots. Blood is taken from a vein.
Before surgery and childbirth, for bruising or bleeding with no clear cause, to check blood thinner medicines, and during pregnancy.
⏱ Duration: the blood draw takes a few minutes; results usually in 1 to 2 days
Be sure to tell your doctor
How to prepare
- Food. Usually the test is done on an empty stomach, 8 to 12 hours after eating. You can drink plain water. Check with your clinic.
- The day before. Do not eat fatty food or drink alcohol. Do not smoke for at least 1 hour before the test.
- Medicines. Do not stop your medicines. If you take medicines for your blood, tell your doctor. The doctor decides what to do.
- Before the draw. Sit quietly for 10 to 15 minutes. Do not rush.
What to bring
- Your referral
- A list of the medicines you take
How it goes
- You sit down and rest your arm on a support
- A band is tightened above your elbow
- The skin is wiped, and a needle goes into a vein
- Blood is collected into one or more tubes
- The needle comes out, and a cotton pad is pressed on the spot
What you'll feel
- A quick prick, like a mosquito bite
- Sometimes you feel a bit dizzy. Tell the nurse
Afterwards
- Press the cotton pad for 3 to 5 minutes. Do not bend your arm
- A bruise can appear. It goes away on its own
- You can eat and go back to your day right away
- Your doctor will explain the results
Common questions
Do I need an empty stomach for a clotting test?
Usually yes, 8 to 12 hours after eating. You can drink water. Your clinic will tell you the exact rules.
What is INR?
It is a measure of blood clotting. It is often checked in people who take blood thinners, to find the right dose.