--- title: "Prothrombin time (PT) and INR: what the test measures, normal levels, and what a high PT or INR means" type: biomarker url: "https://www.test-well.com/biomarkers/prothrombin-time" also_known_as: - prothrombin time - prothrombin time (pt) - pt category: Metabolic Health units: - seconds - sec order_price_usd: 23.99 order_item: Prothrombin Time with INR order_url: "https://www.test-well.com/tests/prothrombin-time-inr" reviewed_at: 2026-09-21 --- # Prothrombin time (PT) and INR: what the test measures, normal levels, and what a high PT or INR means > Prothrombin Time is measured with a standard blood draw; no fasting is needed. A typical reference range is 11.0 – 13.5 seconds. At TestWell it's $23.99 all-in as Prothrombin Time with INR, results in 1–3 business days, drawn at Quest. An out-of-range result is a prompt to look closer, not a diagnosis. Prothrombin time (PT) measures how many seconds your blood takes to form a clot after a clotting trigger is added, testing the liver-made clotting factors that warfarin, vitamin K and liver disease all affect. Most labs report a normal PT of about 11 to 13.5 seconds. The INR is the same result standardized so it reads the same in any lab: roughly 0.8 to 1.1 for someone not on a blood thinner, and usually 2.0 to 3.0 for someone on warfarin. Also known as: prothrombin time, prothrombin time (pt), pt. ## Key facts | Fact | Value | | --- | --- | | Units | seconds / sec | | Sample | Blood draw | | Fasting | Not required | | Results | 1–3 business days | | Price | $23.99 | | Labs | Quest | ## What does a prothrombin time test measure? Blood clots through a chain of proteins called clotting factors, most of them made by the liver. The prothrombin time test takes the liquid part of your blood, adds tissue factor (the trigger your body releases when a vessel is injured) and calcium, and times how long a clot takes to form. That timing depends on five factors in particular: factor VII, factor X, factor V, prothrombin (factor II) and fibrinogen. If any of them is low or not working, the clot forms late and the PT is prolonged. Four of those factors need vitamin K to be made in a working form, which is why PT is the test that tracks warfarin (a vitamin K blocker), vitamin K deficiency and the failing production of a damaged liver. It says nothing about platelets and little about the other half of the clotting cascade, which is tested separately by the partial thromboplastin time (PTT). Because the reagent used to trigger the clot varies between manufacturers, the same blood sample can give a PT of 12 seconds in one lab and 14 in another. The International Normalized Ratio, or INR, fixes that: it divides your PT by the lab's normal PT and adjusts for the reagent's sensitivity, producing a ratio that means the same thing everywhere. Most reports show both numbers; clinicians managing warfarin read the INR. ## Who should get a PT/INR test? The largest group is people taking warfarin. Warfarin has a narrow window between too little effect (clots) and too much (bleeding), and dose requirements shift with diet, other medications and illness, so the INR is checked frequently when a dose is started or changed and then, once stable, roughly every four weeks, with intervals of up to twelve weeks acceptable for people whose readings have stayed steady. Many warfarin patients test at home with a fingerstick meter and report the value to their anticoagulation clinic. PT/INR is also part of the work-up for bleeding that has no obvious cause: bruising easily or in unusual places, nosebleeds that are hard to stop, prolonged bleeding after dental work or a cut, blood in the urine or stool, or heavy periods. It is a standard measure of liver function, because a rising INR shows the liver is no longer making enough clotting factor, and it feeds the scores that stage liver disease. Suspected vitamin K deficiency (poor intake, prolonged antibiotics, malabsorption, newborns), disseminated intravascular coagulation in acutely ill patients and a family history of a clotting-factor disorder are the other common reasons. Surgeons and proceduralists often request a PT/INR before an operation. Guidelines from the British Society for Haematology note that routine clotting screens in people with no bleeding history do not predict surgical bleeding well and are not recommended as a blanket rule, but many hospitals and outpatient procedure centers still require the result, and it is a reasonable pre-op check for anyone with liver disease, a bleeding history or a blood-thinning medication. ## How to get a PT/INR test and prepare for it PT with INR can be ordered by your doctor or anticoagulation clinic, or online through TestWell for a draw at a Quest or Labcorp patient service center, with a licensed physician reviewing the order and results in your portal within a few business days. It is available on its own, paired with PTT as a full clotting screen, or inside a blood clotting panel; the paired version is the one to choose for unexplained bleeding, because the pattern across both tests is what points to a cause. No fasting is needed. The sample is drawn into a light-blue citrate tube that must be filled to its line and mixed properly, and it has to be tested within about a day, so a walk-in lab is a better setting than a mailed kit. Tell the ordering physician about every medication and supplement: warfarin, direct oral anticoagulants (apixaban, rivaroxaban, dabigatran), heparin, antibiotics, and supplements such as vitamin K, fish oil, high-dose vitamin E, cranberry, ginkgo and St John's wort, all of which can move the result. If you take warfarin, keep your routine the same before the test: take the dose at your usual time, do not change how much leafy-green vegetable you eat that week, and avoid a heavy alcohol intake the night before. The point of the INR is to see the effect of the dose you are actually taking, so the sample should reflect an ordinary day. ## What is the normal range for Prothrombin Time? | Population | Reference range | | --- | --- | | age 18+ | 11.0 – 13.5 seconds | Reference intervals differ slightly between labs; the range printed on your report is the one to interpret against. Ranges are usually set so 95% of healthy people fall inside them. ## Normal PT and INR levels, and warfarin INR targets A typical adult prothrombin time is about 11 to 13.5 seconds; your report will show the range for the reagent your lab uses, which may run a second or so either side. For someone not taking an anticoagulant, a normal INR is roughly 0.8 to 1.1. An INR above about 1.2 to 1.3 in a person on no blood thinner is the point at which clinicians start looking for a reason, and readings above 1.5 in liver disease or before a procedure carry weight in decisions. For people on warfarin the goal is deliberately abnormal. The CHEST antithrombotic guidelines set an INR target of 2.0 to 3.0 for most indications, including atrial fibrillation, deep vein thrombosis and pulmonary embolism. The 2020 ACC/AHA valve guideline sets 2.5 to 3.5 for mechanical mitral valves and for mechanical aortic valves with additional risk factors, and 2.0 to 3.0 for an uncomplicated mechanical aortic valve. Your prescriber will tell you which range is yours; a reading inside it is a normal result for you, even though the lab flags it as high. Two cautions on reading the number. PT and INR are not a reliable measure of the direct oral anticoagulants; rivaroxaban and edoxaban can prolong PT somewhat and apixaban barely moves it, so a normal INR does not mean one of these drugs has worn off. And a slightly long PT with a normal PTT in someone who is otherwise well is often an early sign of low vitamin K or mild liver strain rather than a bleeding disorder; the section on what happens after an abnormal result covers the follow-up. | Situation | Usual INR target or range | Source | | --- | --- | --- | | Not taking an anticoagulant | About 0.8–1.1 | Lab reference range (MedlinePlus, Testing.com) | | Atrial fibrillation on warfarin | 2.0–3.0 | CHEST 2012 antithrombotic guidelines | | DVT or pulmonary embolism on warfarin | 2.0–3.0 | CHEST 2012 antithrombotic guidelines | | Mechanical aortic valve, no other risk factors | 2.0–3.0 | 2020 ACC/AHA valvular heart disease guideline | | Mechanical mitral valve, or aortic valve with risk factors | 2.5–3.5 | 2020 ACC/AHA valvular heart disease guideline | _Targets are the guideline defaults; the prescriber sets the individual range. Direct oral anticoagulants are not monitored with INR._ ## High PT or INR: what a prolonged clotting time usually means The most common reason for a high INR is the intended one: warfarin. When the INR climbs above the target range the usual causes are a new medication that interacts (many antibiotics, amiodarone, some antifungals, and high doses of acetaminophen are frequent culprits), an illness with poor eating, a drop in vitamin K intake, alcohol, or a dosing mix-up. An INR that is a little above range without bleeding is common and managed by the anticoagulation clinic; a very high INR, or any INR with bleeding, needs a same-day call. In someone not on warfarin, the causes in rough order of frequency are vitamin K deficiency (poor diet, prolonged antibiotics that clear the gut bacteria that make vitamin K, fat malabsorption from celiac disease, bile-duct obstruction or pancreatic insufficiency), liver disease (the liver simply makes fewer factors, so PT rises as function falls and is a sensitive short-term marker of how sick a liver is), and disseminated intravascular coagulation, in which widespread clotting in a critically ill patient consumes the factors. Direct oral anticoagulants, particularly rivaroxaban, can also prolong PT. Rarer causes include an inherited or acquired deficiency of a single factor. Factor VII deficiency is the classic finding when PT is long but PTT is normal; deficiencies of X, V, II or fibrinogen lengthen both tests. A sample problem is always on the list too: an under-filled citrate tube, a very high hematocrit, or a sample that sat too long can all produce a falsely long PT, which is why an unexpected result is repeated before anything is concluded. ## Short PT or low INR: usually not a problem A PT below the reference range, or an INR under 0.8, rarely means anything on its own. It can follow a recent vitamin K-rich diet or supplement, reflect a naturally high factor VII level, or appear early in disseminated intravascular coagulation before the factors are used up. In someone on warfarin, a low INR is the meaningful version: the dose is not protecting against clots, and the prescriber usually adjusts it and rechecks within days. A short PT does not by itself indicate a clotting tendency, and the inherited conditions that do raise clot risk (factor V Leiden, prothrombin gene mutation, antiphospholipid antibodies) are looked for with their own tests, not with PT. If a low result comes with a personal or family history of unexplained blood clots, that separate thrombophilia work-up is the right next step. ## PT vs PTT: reading the two clotting tests together PT and PTT test different halves of the clotting cascade and are most useful side by side. PT covers the extrinsic and common pathways (factors VII, X, V, II and fibrinogen) and tracks warfarin, vitamin K and the liver. PTT covers the intrinsic pathway (factors VIII, IX, XI and XII) plus the same common pathway, and tracks heparin, hemophilia A and B, von Willebrand disease and the lupus anticoagulant. The pattern narrows the search quickly. A long PT with a normal PTT points to factor VII: early warfarin effect, early vitamin K deficiency, early liver disease or a factor VII deficiency. A normal PT with a long PTT points to heparin, hemophilia, von Willebrand disease or a lupus anticoagulant, the last of which paradoxically raises clot risk. Both prolonged points to the shared pathway or to a global problem: significant liver disease, severe vitamin K deficiency, a warfarin overdose, disseminated intravascular coagulation, or a deficiency of factor X, V, II or fibrinogen. | PT | PTT | Points toward | | --- | --- | --- | | Long | Normal | Factor VII: early warfarin effect, early vitamin K deficiency or liver disease, factor VII deficiency | | Normal | Long | Heparin, hemophilia A or B, von Willebrand disease, lupus anticoagulant, factor XI or XII deficiency | | Long | Long | Liver disease, severe vitamin K deficiency, warfarin overdose, DIC, deficiency of factor X, V, II or fibrinogen | | Normal | Normal | Clotting factors are working; bleeding, if present, is more likely a platelet or vessel problem | _Typical patterns for an initial read; a mixing study and factor assays confirm the cause._ ## What happens after an abnormal PT or INR On warfarin, an out-of-range INR goes to the anticoagulation clinic or prescriber the same day. Small excursions are handled by adjusting the dose and rechecking within about a week; a markedly high INR may be managed by holding doses or with vitamin K, and any bleeding, black or bloody stools, blood in the urine, a severe headache or a fall on a high INR is an emergency. The CHEST guidelines describe the thresholds clinicians use; the decisions are theirs, not something to work out from the number alone. Off warfarin, the first step for an unexpectedly high result is a repeat on a properly filled sample together with a PTT, a liver panel and a complete blood count with platelets. A long PT that corrects when the sample is mixed with normal plasma points to a factor deficiency and prompts factor assays or a trial of vitamin K under a clinician's direction; one that does not correct suggests an inhibitor such as a lupus anticoagulant. Persistent unexplained prolongation, or any prolongation with bleeding, is a hematology referral. Mild elevations that resolve after vitamin K or after an antibiotic course ends need nothing further beyond a recheck. ## What does a high Prothrombin Time mean? Often reflects warfarin therapy, vitamin K deficiency, or liver disease. ## How do you get tested for Prothrombin Time? | Order | Type | Price | Includes | | --- | --- | --- | --- | | [Prothrombin Time with INR](https://www.test-well.com/tests/prothrombin-time-inr) | Single test | $23.99 | This marker | | [Blood Clotting Panel](https://www.test-well.com/tests/blood-clotting-panel) | Panel | $149.99 | 4 tests | ## Quest vs Labcorp vs BioReference | Lab | Available | Price | Notes | | --- | --- | --- | --- | | Quest Diagnostics | Yes | $23.99 | Choose Quest at checkout; walk-in patient service centers in every state TestWell serves outside NY and NJ. | | Labcorp | No | — | Not offered through Labcorp for this test. | | BioReference (NY & NJ) | No | — | Not available in NY/NJ for this test. | - [What a high Prothrombin Time means (causes, symptoms, next steps)](https://www.test-well.com/biomarkers/prothrombin-time/high) ## Common questions about Prothrombin Time ### What is a normal prothrombin time? About 11 to 13.5 seconds for most adult reference ranges, though each lab's range depends on the reagent it uses. The INR standardizes the result: roughly 0.8 to 1.1 is normal for someone not taking a blood thinner. ### What is a normal INR for someone on warfarin? For most indications, including atrial fibrillation and blood clots in the legs or lungs, the target is 2.0 to 3.0. Mechanical mitral valves, and aortic valves with extra risk factors, use 2.5 to 3.5. Your prescriber sets your individual range; within it, a lab-flagged 'high' INR is normal for you. ### What is the difference between PT and INR? PT is the raw clotting time in seconds and varies with the lab's reagent. INR is that time divided by the lab's normal and corrected for reagent sensitivity, giving a ratio that reads the same in every lab. Warfarin is managed by INR for that reason. ### Do I need to fast for a PT/INR test? No. Keep your normal routine, including your usual warfarin dose and your usual diet, so the result reflects an ordinary day. Tell the ordering physician about all medications and supplements, since antibiotics, fish oil, vitamin K, cranberry and several herbal products can shift the result. ### Does PT/INR measure Eliquis, Xarelto or Pradaxa? Not reliably. Direct oral anticoagulants affect PT unpredictably — rivaroxaban and edoxaban may prolong it, apixaban barely changes it — so a normal INR does not mean the drug has worn off. These medicines are not monitored with routine INR; specific anti-Xa or dilute thrombin time assays are used when a level is needed. ### Do I need a doctor's order to test my prothrombin time? No. TestWell's licensed physician network reviews and approves your order — usually within minutes. You can place an order online without an in-person visit or a referral from your own doctor. ### How long does it take to get Prothrombin Time results? Most Prothrombin Time results are available in 1–3 business days after your specimen arrives at the lab. You'll get an email the moment your results are ready, with everything viewable in your TestWell portal. ### How much does a Prothrombin Time test cost? Our Prothrombin Time with INR starts at $23.99. That's the all-in price — no copays, no insurance hoops, no surprise bills. HSA and FSA cards are accepted. ### Do I need to fast before my Prothrombin Time test? Fasting is not required for the Prothrombin Time test. You can have your blood drawn any time of day. ### Which lab will process my Prothrombin Time test? Your test will be processed by Quest Diagnostics, Labcorp, or BioReference depending on which is closest to you and which lab carries the test. All three are CLIA-certified and trusted by hospitals nationwide. You'll choose your lab during checkout from 4,000+ locations. ## Keep reading - [PT/INR Explained: What the Prothrombin Time and INR Blood Test Measures and What Your Result Means](https://www.test-well.com/guides/pt-inr-explained) - [How to Read Your Blood Test Results](https://www.test-well.com/guides/how-to-read-your-blood-test-results) - [Liver Function Tests Explained: What a Liver Panel Shows and When to Get One](https://www.test-well.com/guides/liver-function-tests) - [Easy bruising: which blood tests?](https://www.test-well.com/symptoms/easy-bruising) - [Heavy periods: which blood tests?](https://www.test-well.com/symptoms/heavy-periods) - [Fatigue: which blood tests?](https://www.test-well.com/symptoms/fatigue) - [Before your test: Common medications](https://www.test-well.com/prep/medications) - [Before your test: Alcohol](https://www.test-well.com/prep/alcohol) - [Before your test: Fasting](https://www.test-well.com/prep/fasting) - [Before your test: Recent illness](https://www.test-well.com/prep/recent-illness) ## Sources - [AACC Lab Tests Online](https://www.testing.com/tests/prothrombin-time-and-international-normalized-ratio-pt-inr/) - [MedlinePlus (NIH) — Prothrombin Time Test and INR (PT/INR)](https://medlineplus.gov/lab-tests/prothrombin-time-test-and-inr-ptinr/) - [Holbrook A, et al. Evidence-Based Management of Anticoagulant Therapy — CHEST Antithrombotic Guidelines, 9th ed. (2012)](https://doi.org/10.1378/chest.11-2295) - [Otto CM, et al. 2020 ACC/AHA Guideline for the Management of Patients With Valvular Heart Disease](https://doi.org/10.1161/CIR.0000000000000923) - [Chee YL, et al. British Society for Haematology — Guidelines on the assessment of bleeding risk prior to surgery or invasive procedures (2008)](https://doi.org/10.1111/j.1365-2141.2007.06968.x) ## Related biomarkers - [Glucose](https://www.test-well.com/biomarkers/glucose) - [Creatinine](https://www.test-well.com/biomarkers/creatinine) - [eGFR](https://www.test-well.com/biomarkers/egfr) - [BUN](https://www.test-well.com/biomarkers/bun) - [ALT](https://www.test-well.com/biomarkers/alt) - [AST](https://www.test-well.com/biomarkers/ast) - [Reference range lookup tool](https://www.test-well.com/tools/reference-range-lookup) - [Lab unit converter](https://www.test-well.com/tools/lab-unit-converter) - [All biomarkers](https://www.test-well.com/biomarkers) --- Medically reviewed by Youmna DiStefano, MD (Medical Reviewer, TestWell); last reviewed 2026-09-21. Review policy: https://www.test-well.com/reviewers/youmna-distefano-md Canonical page: https://www.test-well.com/biomarkers/prothrombin-time Machine-readable catalog: https://www.test-well.com/api/catalog.json · MCP server: https://www.test-well.com/mcp · Overview for agents: https://www.test-well.com/llms.txt Prices are cash-pay, in USD, and include physician authorization; every order adds one flat $6 lab processing fee. Educational content is not a diagnosis — discuss results with a clinician.