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INR blood test

International normalized ratio

In short

A typical adult INR result is 0.8 to 1.1 ratio (not on a blood thinner). Without a blood thinner, an INR above the range can mean the blood is clotting a bit more slowly. On a blood thinner, a result above the personal target can raise the risk of bleeding. Always read your result against the range printed on your own report.

The clotting time (PT), put on a scale that every lab shares.

The INR puts the clotting time (PT) on one shared scale; without a blood thinner, it sits near 1. People who take a blood thinner are given a personal target by their doctor, often 2 to 3. Their result is read against that target instead of the typical range.

Is my INR high or low?

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Typical range

ForRangeUnit
Adults · not on a blood thinner0.8–1.1ratio

Typical ranges for adults. Labs differ a little, so the range printed next to your result is the one to go by.

If your INR is high

Without a blood thinner, an INR above the range can mean the blood is clotting a bit more slowly. On a blood thinner, a result above the personal target can raise the risk of bleeding.

Common reasons

  • Taking a blood thinner, which raises the INR on purpose
  • On a blood thinner: new medicines, illness, or less vitamin K in meals
  • Low vitamin K, from a poor diet, some antibiotics or poor absorption
  • A sample tube not filled fully, or a delay before testing
  • Less often: liver disease, since the liver makes most clotting proteins
  • Less often: DIC, a serious illness in which clotting proteins get used up

If your INR is low

Without a blood thinner, an INR a little below the range is rarely a concern. On a blood thinner, a result below the personal target can mean less protection against clots.

Common reasons

  • Natural variation between labs and testing methods
  • On a blood thinner: missed doses or new medicines
  • On a blood thinner: more vitamin K from food or supplements

What can throw it off

For people on a blood thinner, new medicines, illness, alcohol or diet changes can move the INR within days.

When it can’t wait

A INR of 5 ratio or more usually needs a doctor's attention the same day. Call your doctor’s office, or their after-hours line. If you feel very unwell, call your local emergency number.

Questions to take to your appointment

  1. 1Is my result in line with my own target, if I have one?
  2. 2Could a new medicine, an illness or my diet explain the change?
  3. 3When should my INR be checked again?

Read together with

Doctors rarely read INR alone. These usually sit next to it.

Quick answers

What is the INR blood test?

INR (International normalized ratio): The clotting time (PT), put on a scale that every lab shares. The INR puts the clotting time (PT) on one shared scale; without a blood thinner, it sits near 1. People who take a blood thinner are given a personal target by their doctor, often 2 to 3. Their result is read against that target instead of the typical range.

What is a normal INR level?

For most adults, INR is typically 0.8 to 1.1 ratio (not on a blood thinner). Labs differ a little, so the range printed next to your result is the one to go by.

What does a high INR mean?

Without a blood thinner, an INR above the range can mean the blood is clotting a bit more slowly. On a blood thinner, a result above the personal target can raise the risk of bleeding. Common reasons include taking a blood thinner, which raises the INR on purpose; on a blood thinner: new medicines, illness, or less vitamin K in meals; low vitamin K, from a poor diet, some antibiotics or poor absorption; and a sample tube not filled fully, or a delay before testing. A doctor reads it together with your other results and how you feel.

What does a low INR mean?

Without a blood thinner, an INR a little below the range is rarely a concern. On a blood thinner, a result below the personal target can mean less protection against clots. Common reasons include natural variation between labs and testing methods; on a blood thinner: missed doses or new medicines; and on a blood thinner: more vitamin K from food or supplements.

What can affect my INR result?

For people on a blood thinner, new medicines, illness, alcohol or diet changes can move the INR within days.

When is my INR result urgent?

A INR result of 5 ratio or more usually needs a doctor's attention the same day. Call your doctor's office or their after-hours line. If you feel very unwell, call your local emergency number.

What should I ask my doctor about my INR?

Questions worth taking to the appointment: Is my result in line with my own target, if I have one? Could a new medicine, an illness or my diet explain the change? When should my INR be checked again?

What this page can’t do

It reads each number on its own.

Doctors read results together — ALT with AST, ferritin with hemoglobin, TSH with free T4. A pattern says more than any single flag.

It doesn't know you.

Your age, your medicines, how you feel and your last result all change what a number means.

It doesn't remember.

Close this page and your results are gone. That's on purpose: nothing was ever sent to us.

We also make Vita: Health Coach, an app for those parts. It reads your whole report with your medicines and history in mind, answers follow-up questions in plain words, and keeps your reports in one place — for you and for the people you look after.

Vita: Health Coach on the App Store

Sources

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