Warfarin Counselling – OSCE guide

Warfarin counselling frequently features in OSCE exams and therefore it’s something you need definitely need to practice, ensuring you are aware of the salient points you need to communicate to a patient during a consultation. Check out the warfarin counselling OSCE mark scheme here.

Before beginning

If any information exists (notes, records etc) use this to get a sound understanding of what the patient is using warfarin for and the target INR range; this will help you tailor the consultation to the needs of the patient.

Opening the consultation

  • Introduce yourself
  • Check patient details
  • Check patient’s understanding of what warfarin is and why they have been prescribed it

Patient perceptions, ideas, and concerns

Patient ideas, concerns, and perceptions usually form the basis for the majority of patient-centred consultation models, however, these are particularly important for warfarin counselling so it’s important that you check.

Patients will have heard lots about warfarin since it has been around for many years, and a popular concern that you may come across is patients asking why they have been prescribed “rat poison” – yes that’s right warfarin first came into commercial use as rat poison. To provide reassurance for this particular concern, explain to patients that this is how the medicine was discovered i.e. was manufactured for a completely different reason, but later its value for use in helping treat and prevent conditions in humans became known. Anecdotes such as discovery or penicillin can be used here to put things into perspective.

In addition to this, some patients may already be aware of all the monitoring and dietary requirements prior to the consultation, all of which can be daunting. It is your job to put the patient at ease and highlight the importance of taking warfarin for the condition that is being treated (see below).

How warfarin works

Using patient-friendly language, explain that warfarin works by inhibiting the formation of active clotting factors and so “thins the blood”. Patients find it reassuring to know that the “blood-thinning” can be reversed, so mentioning this at some point during the consultation can be useful. Ensure you explain how it works for the condition being treated e.g. DVT, PE, stroke prevention.

This would also be an appropriate time to explain what INR is INR – international normalised ratio is a measure of how long it takes blood to clot. In healthy people an INR of 1 is normal, however since you are at a high risk for blood clots we want to thin your blood and so your ideal INR should be between 2-3 (this will differ between patients and conditions) i.e. it will take two to three times as long for your blood to clot compared to before.

In order to ensure that we keep your blood within the necessary range we will need to monitor your INR level every so often; this is done through a blood test. The blood tests will initially be frequent (every 3-4 days until two consecutive readings are within range), and then after this, you will be tested twice weekly for 1-2 weeks (again until two consecutive readings within range). Thereafter, testing can increase to longer periods (e.g. every 12 weeks).

Counselling on warfarin use

Since the dose of warfarin varies based on INR this is something that you should also explain to the patient.

Other counselling points about taking warfarin can include:

  • Warfarin should be taken at the same time each day.
  • The strength of tablets come in different colours for ease of recognition (0.5mg white; 1mg brown; 3mg blue; 5mg pink).
  • Never double up on doses: If a dose is accidentally missed, they should continue with the regimen as prescribed, and never take a double dose (unless specifically advised).
  • Let healthcare professionals such as community pharmacies know that you are taking warfarin (due to drug interactions and contraindications etc).
  • Inform anticoagulant clinic if any other medication has been started (by GP, over the counter, herbal, hospital) since it may mean patient needs more frequent drug monitoring. This includes consumption of any vitamins/multivitamins since vitamin E can enhance the effects of warfarin and vitamin K can antagonise the effects of warfarin.
  • Inform the patient of the duration of treatment, since in some cases treatment is only required for a set period (e.g. certain cases of DVT will need treatment for 6 months).

Note: warfarin cannot be used during pregnancy therefore if necessary discuss this with the patient and consider contraceptive options for women of a child-bearing age. Also for women with regular menses, heavy periods whilst on warfarin should be reported to the GP since the dose may need to reviewed or alternative options considered (change of drug, initiation of iron etc.)

Lifestyle advice


Drastic changes in diet, especially an increase in consumption of foods high in vitamin K (such as broccoli, kale, or spinach) can potentially affect control of anticoagulation. If the patient ever wishes to change diet then they should inform the anticoagulant clinic so necessary dose adjustments and monitoring requirements can be fulfilled.


Limit the amount of alcohol to a maximum of one or two drinks a day (within nationally recommended range for gender), and advise to never binge drink. If there are major changes in alcohol consumption (patient stops drinking, or starts drinking more) then INR can be affected; the anticoagulant team should, therefore, be notified.

Cranberry juice

Cranberry juice is a specific food that is known to interact with warfarin by enhancing the anticoagulant effect. Cranberry juice, therefore, should be avoided. Grapefruit juice is also known to interact with warfarin but effects are not as serious as cranberry juice; this should also ideally be avoided.


Take extra care when carrying out routine tasks such as brushing teeth or shaving; a soft toothbrush or an electric razor can help. For dental appointments, inform the dentist whilst booking just in case you need to stop the warfarin for a few days before a procedure.

Yellow books and alert card

At the start of treatment all patients should be provided with two yellow anticoagulant books; blood monitoring book and patient information book. In addition to this, the patient should also be given an anticoagulant alert card.

The patient should always carry the anticoagulant alert card with them in case of an emergency and always take the yellow blood monitoring book with them to each appointment at the anticoagulant clinic and if possible to other appointments (e.g. GP, pharmacy reviews, dental appointments etc).

The patient information book is a useful resource since it provides the patient with a point of reference and reinforces what has been covered in this Geeky Medics guide. If you are the healthcare professional who is providing the information booklet (and other resources) then please ensure all fields are filled.

Closing the consultation:

By this point, the patient will have had lots of information to grasp so give them to ask the opportunity to ask any questions to clarify (your consultation model may have involved questions throughout so this may not be necessary here)

If you feel as though the patient would benefit from a recap session, arrange a follow-up appointment (face-to-face or telephone) and also direct the patient to the yellow anticoagulant information booklet.

Safety netting

  • Bleeding rules; report any spontaneous bleeding that does not stop. As a rule of thumb, if there is a “minor bleed” e.g. light nosebleed, and this does not stop 10 minutes after pressure has been applied, the patient should seek medical help. Inform the patient about how to recognise serious side effects such as gastrointestinal bleeds and severe headaches (e.g. subarachnoid haemorrhage)
  • Bruising: The patient is more likely to bruise, they need to know this and be careful. They would be advised to give up any heavy contact sports (e.g. rugby, boxing etc)
  • Patients should report any of the following: severe back pain (could be indicative of spontaneous retroperitoneal bleeding); difficulty breathing or chest pain (could be indicative of pulmonary embolism); or report any symptoms that could be a sign of the condition that you are treating (e.g. pain in the calf as this could be indicative that the INR is not within the required range).

Finish off by checking what the patient feels about the warfarin now that you have explained everything to them. If they are still not happy, then warfarin may just not be the drug for them, and other options do exist e.g. NOACs. Pros and cons of these can be explained if needed.

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