How does warfarin affect inr

PT stands for prothrombin time. A typical INR target ranges from but can vary from patient to patient. Patients with a tendency towards clotting may have a range targeting , whereas patients with a higher bleeding risk may have a lower INR between According to the American Heart Association AHA , patients should be tested at least once a month, but some patients will require testing as often as twice a week.

INR tests can be done at a lab or clinic but can also be done at home for some patients. Home testing requires the use of an in-home INR monitoring machine and test strips. After self-testing with this device, you can report your INR results to your care team to determine if you need to adjust your warfarin dose. Learn more about home testing here or talk to your healthcare provider.

If you miss any doses, you should contact your healthcare provider and ask about how to safely restart it. You also need to make sure that your doctor always has an up-to-date list of all the medications you take since some medications may interact with warfarin.

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If your learning was spontaneous, please click:. Oral anticoagulants: mechanism of action, clinical effectiveness, and optimal therapeutic range. Oral anticoagulant therapy: important information for patients. Guidelines on oral anticoagulation with warfarin - fourth edition.

British Journal of Haematology ;— Bridging anticoagulation: perioperative management of patients on anticoagulants. Clinical Pharmacist ; Perioperative management of antithrombotic therapy: antithrombotic therapy and prevention of thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest ;eS—S. Subtherapeutic oral anticoagulant therapy: frequency and risk factors. Thrombosis and Haemostasis. Treating acute diarrhoea in adults.

The Pharmaceutical Journal. Understanding low INR in clinical practice. Vitamin K intake and sensitivity to warfarin in patients consuming regular diets. PMID: Influence of regular physical activity on warfarin dose and risk of hemorrhagic complications: physical activity and warfarin response.

Pharmacotherapy ;34 6 — Increased sensitivity to warfarin after heart valve replacement. Ann Pharmacother. SIGN Antithrombotics: indications and management. A national clinical guideline.

Thromboembolic and bleeding complications in patients with mechanical heart valve prostheses. Circulation ;89 2 — Effect of a simple two-step warfarin dosing algorithm on anticoagulant control as measured by time in therapeutic range: a pilot study. Journal of Thrombosis and Haemostasis. Guidelines on the management of valvular heart disease. European Heart Journal. Access provided by. How to identify causes of a subtherapeutic INR Pharmacists and healthcare professionals are often involved in the management of patients with subtherapeutic international normalised ratios INRs , the cause of which is important to identify because this will affect decisions and the subsequent management of the patient.

Warfarin is indicated for, among other things: Treatment of acute venous thromboembolism VTE , e. Table 1: Examples of typical target international normalised ratio INR values. Causes of a subtherapeutic INR Pharmacists and healthcare professionals are often involved in the management of both inpatients and outpatients with subtherapeutic INRs.

A missed dose of warfarin is usually reflected in the INR result two to five days after the missed dose, 12 although a response may be seen within 16 hours. In many cases, no explanation may be found for unstable INR values. It may be worthwhile discussing aspects of the dosing regimen. Changes in the INR may also be the result of occult causes, such as undisclosed drug use, lifestyle and medical causes. Computerised decision support is a very useful tool for maintaining therapeutic INR levels in patients receiving anticoagulant treatment.

There is evidence that computerised decision support can achieve improved therapeutic control in terms of INR, when compared with human performance.

A best practice Decision Support module has been developed for managing warfarin treatment, based on data from the Coventry system, 17 which has been widely accepted internationally. This module is available free to General Practices in New Zealand. It enables clinicians to more easily adjust oral anticoagulant doses and schedule follow-up consultations.

INR results can be tracked and monitored over time and a dose calendar can be printed for the patient. A meta-analysis of randomised controlled trials compared computerised decision support methods of determining warfarin dosage with traditional manual methods in patients.

A randomised controlled trial compared the INR control by the percentage of time within-target of two groups of patients attending an anticoagulation clinic in Italy. One of the advantages of computerised decision support tools is that information can be easily retrieved, providing many opportunities for clinical practice audit, including identifying patients who are on anticoagulant treatment but are not receiving INR monitoring.

Transfer of the care of a patient on warfarin treatment from secondary to primary care is associated with a high risk for several reasons:. Some New Zealand hospitals have developed protocols for the timely transfer of information about warfarin therapy to primary care on patient discharge. Essential details have been found to be:. New Zealand hospitals use a variety of warfarin initiation protocols and there is little evidence that one is any better than another.

It is recommended to follow on with the protocol initiated in secondary care for patients who start warfarin in this environment. It would be helpful for primary care clinicians to become familiar with local hospital protocols. Follow us on facebook. Decision support for health professionals ». South Island general practice support ». Practice acquisition and careers in health ».

Click here to register ». Forgot your login? Login to my bpac. Remember me. Haematology Medicines management. Use of INR for monitoring warfarin treatment Regular measurement of INR levels is an essential component in the management of patients receiving warfarin treatment. In this article INR monitoring is essential for all patients treated with warfarin Managing warfarin treatment Computerised decision support Guide for over anti-coagulation 18 Transfer of care across the primary — secondary interface is associated with a high risk References In this article.

Key concepts: INR measurement is a key component in maintaining good control of warfarin treatment Practices should have clearly understood mechanisms in place to monitor patients treated with warfarin, to minimise the risks and maximise the benefits There is evidence that computerised decision support can achieve improved therapeutic control.

INR monitoring is essential for all patients treated with warfarin International Normalised Ratio INR testing is well established as an integral part of warfarin treatment. INR levels can be difficult to control Although regular testing of INR levels is essential for all people taking warfarin to maintain control of the INR, in practice, INR levels show considerable intra-patient variability. Maintaining good systems is important It is important that practices develop a standardised management protocol for all patients treated with warfarin, in order to optimise health outcomes, by achieving tighter control.

Managing alterations in the INR Some fluctuations in INR level can be expected, and for minor variations, changes in weekly doses are usually not required. Changes in the INR level in a usually stable patient may be due to a number of reasons, including: 7,8 Major changes in diet or alcohol intake Drug interactions pharmaceutical or complementary Systemic or concurrent illness Non-adherence to dosage regimen Unknown causes. Diet or alcohol Patients on warfarin are usually advised to consume a reasonably consistent proportion of vitamin K rich foods such as broccoli, spinach and cabbage.

Drug interactions Many medicines and herbal products can interact with warfarin. Pregnancy Warfarin is not recommended during pregnancy. Travel Check with your healthcare provider if you expect to travel.

Never double a dose because you missed a dose. Do tell your healthcare provider when you get sick or hurt. Do take warfarin exactly as prescribed. Do tell anyone giving you medical or dental care that you are taking warfarin. Do keep appointments for blood tests. Warfarin Interacts With Other Medications Patients who take warfarin should consult with their healthcare provider before taking any new medication, including over-the-counter nonprescription drugs, herbal medicines, vitamins or any other products.

Patients undergoing warfarin therapy should avoid drinking alcohol on a daily basis. Alcohol should be limited to no more than 1 to 2 servings of alcohol occasionally.

This means an average of one to two drinks per day for men and one drink per day for women. A drink is one 12 oz. The antiplatelet effect of alcohol increases the risk of major bleeding, even if the INR remains within the target range. Foods - Some foods can interfere with the effectiveness of warfarin. The most important point to remember is to eat what you normally eat and not to make any major changes in your diet without contacting your healthcare provider.

Vitamin K - Eating an increased amount of foods rich in vitamin K can lower the PT and INR, making warfarin less effective and potentially increasing the risk of blood clots. Patients who take warfarin should aim to eat a relatively similar amount of vitamin K each week.

The highest amount of vitamin K is found in green and leafy vegetables such as broccoli, lettuce, and spinach. It is not necessary to avoid these foods; however, it is important to try to keep the amount of vitamin K you eat consistent. Download our quick reference guide to foods that are high and low in Vitamin K. PDF Wear Medical Identification Those who require long-term warfarin should wear a medical alert bracelet, necklace, or similar alert tag at all times.

Where to Get More Information Your healthcare provider is the best source of information for questions and concerns related to your medical problem. Last Reviewed: Sep 30,