Skip to content
Blood Test Tracker

INR (International Normalized Ratio)

A standard way to report how long your blood takes to clot, used mainly to monitor warfarin and to check clotting and liver function.

AI-drafted. Awaiting verificationAlso called INRLOINC 6301-6

Check your result

Sex (optional)

Type your result to see where it falls.

Nothing you type here leaves your browser.

What it is

INR stands for International Normalized Ratio. It is worked out from the prothrombin time (PT), the number of seconds your blood takes to clot, in a way that lets results be compared between labs. Without blood thinners, a typical INR is about 1.0 (Mayo's range is 0.9–1.1). Warfarin raises it on purpose. The usual warfarin target is 2.0–3.0, and a higher target of 2.5–3.5 is used for some people.

Why it matters

For people on warfarin, the INR is the main check that the dose is working as intended. Too low can leave clot risk uncovered, and too high raises the chance of bleeding. For people not on warfarin, a raised INR can be an early sign that the liver or the vitamin K supply is not keeping up with the clotting proteins the body needs.

If it’s low

For someone not on warfarin, an INR a little under 0.9 is rarely a concern. For someone on warfarin, an INR below target means less warfarin effect than intended, and clinics watch for a higher chance of blood clots when the INR is under 2.0.

Common causes

  • Missed or late warfarin doses
  • Eating more vitamin K than usual
  • Medicines or supplements that weaken the effect of warfarin
  • Normal variation between tests and labs

What can help

  • Tell your clinic about missed doses, new medicines or diet changes
  • Ask your clinic when the test should be repeated

If it’s high

A higher INR means your blood takes longer to clot. For people on warfarin, a rise above target is common and is usually handled by the clinic that manages the warfarin. Bleeding risk climbs noticeably once the INR is above about 4.5. For people not on warfarin, a high INR can point to a low vitamin K supply, liver problems or low clotting factors.

Common causes

  • On warfarin: a dose change, a missed or doubled dose, or a new medicine or supplement that strengthens warfarin
  • On warfarin: alcohol, or a change in vitamin K intake such as eating fewer leafy greens
  • A sample problem, such as an underfilled tube or late processing
  • Vitamin K deficiency, for example from poor intake or poor fat absorption
  • Liver disease, which lowers the clotting proteins the liver makes
  • Direct oral anticoagulants, which can lengthen the PT even though the INR is not a valid way to measure them
  • DIC (disseminated intravascular coagulation) in people who are seriously ill

What can help

  • If you take warfarin, tell your warfarin clinic about any new medicine, supplement, illness or diet change. Dose changes are made by your clinic
  • Ask your clinic whether you should keep your vitamin K intake about the same from week to week
  • If you are not on warfarin, ask whether liver tests or a vitamin K check would help explain a high INR

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 0.9–1.1 INR. Source: Mayo Clinic Laboratories (Extended Catalog), ARUP Laboratories, MedlinePlus (National Library of Medicine). Labs treat above 5 INR as urgent.

What can affect your result

  • Warfarin dose and timing, and missed doses
  • Vitamin K in your diet, alcohol, and other medicines and supplements
  • Liver disease and vitamin K deficiency
  • The lab's PT reagent and its ISI value
  • Direct oral anticoagulants, for which the INR is not valid
  • Sample collection and handling, including tube fill and hematocrit above 55%
  • Warfarin dose changes, missed doses, and many medicines and supplements change the INR. Alcohol, foods high in vitamin K (such as green leafy vegetables), soybean and canola oils, and high-fat diets can too.
  • If you take warfarin, ask your clinic whether to take your usual dose before or after the test.
  • Direct oral anticoagulants such as rivaroxaban and apixaban can lengthen the PT, but the INR was designed for warfarin and is not a valid way to measure them.
  • Sample problems, such as an underfilled citrate tube, a hematocrit above 55%, or processing delays, can change the result.
  • Finger-stick (point-of-care) meters measure the same thing, and a review found their accuracy generally comparable to lab testing.

Several days after a warfarin dose change. When warfarin is started, it can take days to weeks to settle at a steady level.

When to talk to a clinician

Contact the clinic that manages your warfarin the same day if your INR is 5.0 or higher, even if you feel well. Get emergency care right away for heavy or unstoppable bleeding, vomiting blood, black or bloody stools, blood in your urine, a severe headache, a fall or head injury, or sudden weakness, confusion or trouble speaking.

Questions you could ask

  • What INR range is my target, and why?
  • How often should my INR be checked?
  • If I am not on warfarin, what could explain this result, and do my liver or vitamin K need to be looked at?
  • What do you think caused my INR to rise, and when should I be retested?
  • Could a new medicine, supplement, food change or illness explain it?
  • Which bleeding signs should I watch for?

Questions people ask

My INR is a little above 1.1 and I do not take warfarin. Is that a problem?

Limits differ a little between labs and reagents, so a small difference from a range is common. A clearly raised INR can reflect a low vitamin K supply, liver problems or low clotting factors, so it is worth discussing with a clinician, who can look at your whole picture.

Is a finger-stick INR the same as a lab INR?

Finger-stick meters measure the same thing, and a review of point-of-care testing found its accuracy and precision generally comparable to lab testing. If a meter result is unexpected, your clinic may check it with a lab test.

Why is my warfarin target different from someone else's?

The target depends on why warfarin was prescribed. Labs describe 2.0–3.0 as the standard-intensity range and 2.5–3.5 as the high-intensity range. Your clinician sets yours.

Show the science and sources

Is a change real?

INR naturally varies about 2.5% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 8% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Systematic review and meta-analysis of within-subject and between-subject biological variation data of coagulation and fibrinolytic measurands (Hollestelle MJ et al.).

For clinicians and researchers

The INR is calculated as the patient's PT divided by the mean normal PT (MNPT, the geometric mean of at least 20 healthy people) raised to the power of the International Sensitivity Index (ISI) assigned to the PT reagent against the WHO reference preparation. Recombinant thromboplastins with an ISI under 1.2 are recommended, and an ISI specific to the reagent and analyzer combination gives the best accuracy. The system was developed to standardize monitoring of vitamin K antagonists, so it is not valid for rivaroxaban or apixaban, whose PT results cannot be converted to an INR. Mayo gives a range of 0.9–1.1 for the INR (PT 9.4–12.5 seconds) and describes warfarin ranges of 2.0–3.0 (standard intensity) and 2.5–3.5 (high intensity); ARUP uses the same two ranges. Bleeding risk rises significantly above an INR of 4.5, and thrombotic complications should be considered below 2.0. ARUP's critical value is 5.0 or higher, and the Croatian recommendations call an INR above 5.0 clinically relevant. Point-of-care whole-blood meters are held to the same calibration standards as lab methods, and a review found their accuracy generally comparable. The INR is also used in liver severity scores such as MELD. Recommended recall after an out-of-range INR is within 7 days if above 4.0 or below 1.5, and within 14 days if 3.1–3.9 or 1.6–1.9.

LOINC 6301-6 (primary), 34714-6, 46418-0, 38875-1. Specimen: plasma.

Sources

  1. Prothrombin Time, Plasma (test PTTP), including INR, Mayo Clinic Laboratories (Extended Catalog)
  2. Prothrombin Time/International Normalized Ratio (ARUP test 0030224), ARUP Laboratories
  3. Critical Values List (CORP-APPEND-0104A, Rev. 46, April 2026), ARUP Laboratories (2026)
  4. Croatian Society of Medical Biochemistry and Laboratory Medicine: National recommendations for blood collection, processing, performance and reporting of results for coagulation screening assays prothrombin time, activated partial thromboplastin time, thrombin time, fibrinogen and D-dimer, Biochemia Medica (2019)
  5. Measurement of non-VKA oral anticoagulants versus classic ones: the appropriate use of hemostasis assays, Thrombosis Journal (2014)
  6. Prothrombin Time Test and INR (PT/INR), MedlinePlus (National Library of Medicine)

AI-drafted. Awaiting verification. Last reviewed 2026-10-03. How we build and check these pages.

Related markers