Warfarin is used to decrease the tendency for blood clots or as secondary prophylaxis (prevention of further episodes) in those individuals that have already formed a blood clot .  Warfarin treatment can help prevent formation of future blood clots and help reduce the risk of embolism (migration of a thrombus to a spot where it blocks blood supply to a vital organ. It is very important to monitor warfarin levels in patients blood.

This clinic is set up to best international standards using the Rosendaal linear interpolation method with computer decision support software and is under constant review. Prior to the introduction of the decision support software there were 13 steps involved in INR testing involving patients, nurses and GPs, laboratory and secretarial time. This was reduced to 4 steps in the new system which is less time consuming for patients.

Quality Control

There are a number of quality control processes used by the 4th Practice Warfarin Clinic to verify our results apart from the daily controls which are performed on the testing equipment.


UK NEQAS for Blood Coagulation is an international External Quality Assessment (EQA) programme offering independent impartial assessment of performance with a comprehensive range of coagulation testing for laboratories and individuals worldwide. UK NEQAS for Blood Coagulation programmes are hosted at the Royal Hallamshire Hospital, part of Sheffield Teaching Hospitals NHS Foundation Trust.

The purpose of UK NEQAS for Blood Coagulation is to provide external quality assessment (EQA) for tests of blood coagulation, and other tests of haemostasis, and so promote high standards of performance and practice. EQA, together with internal quality control (IQC) procedures, are seen as vital components of overall laboratory quality assurance.

For the hospital based programme, although participation is predominantly from clinical laboratories, participation by industrial and other laboratories is welcomed. Most participating laboratories are sited within the UK, but registration is open to laboratories in Europe and further afield, whether government supported, private or commercial. UK NEQAS for Blood Coagulation is run on a not for profit basis, under the auspices of UK National External Quality Assessment Service and professional bodies.  Participants in the Point of Care programmes come from both primary and seconday care sectors.

Currently, samples for over 30 different tests of haemostasis are distributed to more than 1,000 participants in the laboratory based programme and over 3,000 participants in the Point of Care Testing (POCT) programme

By providing external quality assessment for tests of blood coagulation carried out on instrument systems designed for near patient testing (NPT) or point of care testing (POCT), as a part of the overall quality assurance, the programme aims to promote high standards of performance and practice, achieved with the UK NEQAS primary aim of education, by provision of independent, objective and impartial information. For further information on NEQAS please see http://www.ukneqas.org.uk/

2. Cork University Hospital.

A number of venous samples are sent to CUH for comparison with the 4th Practice INR results. The results show consistency between the two centres.

Appointments for the 4th Practice Warfarin Clinic are available every day Monday to Friday from 8am to 1pm. Please phone 022-52944 to make an appointment.

Warfarin Therapy and Food

Warfarin is an anticoagulant medication. Some health conditions can cause the blood to clot too much. If this happens, blood clots can form and may block blood flow in the body. This can cause a heart attack, stroke, deep vein thrombosis and other serious health problems. If your blood clots too much, your doctor may prescribe warfarin which makes your blood clot slower. Certain foods and medication can affect how your warfarin works. This handout will help you plan your food choices when taking warfarin.

Vitamin K has the opposite effect of warfarin and helps your blood to clot more quickly. Your warfarin dose will be balanced with the amount of vitamin K in your usual diet to make your blood clot at a safe rate.

The International Normalized Ratio (INR) measures the rate at which blood forms clots. A number of factors can affect your INR, including the vitamin K in your diet. The aim is to consume a similar amount of vitamin K each day.

If you eat more vitamin K than usual, it decreases the effect of warfarin. Your INR will go down and your risk of clotting will increase. If you eat less vitamin K than usual, this will increase the effect of warfarin. Your INR will go up, and your risk of bleeding will increase.

It is important for good health to eat a healthy diet. The main sources of vitamin K in the diet are green leafy vegetables. There is no need to avoid green leafy vegetables, just be careful not to vary your intake too drastically. Vitamin K is important for bone health so do not avoid it all together.

To keep your warfarin working well:

  • Pay attention to how often and how much of vitamin K rich foods you eat and try to keep the portions the same every day.
  • Avoid large changes in the amount of vitamin K you eat:
    • If you eat green leafy vegetables, do not eat a lot one day and none the next.
    • If you do not normally eat green leafy vegetables, do not suddenly eat a large amount of them.
  • Tell your doctor/ warfarin nurse if you plan to make significant changes to your diet. Your INR may be monitored more often for a few weeks, and your warfarin dose may be adjusted, if necessary.
  • Talk to your doctor/ warfarin nurse before eating natto (fermented soybean), cranberries, cranberry juice and tablets/ supplements, grapefruit and grapefruit juice, seville or tangelo oranges, mangoes and their juices. These foods effect the way warfarin works.
  • Stick with one brand of food, in similar amounts to avoid changes in your care. Occasionally different makes or brands contain different amounts e.g. soya and soya protein products e.g. soya milk and tofu.
  • Avoid ‘crash’ or ‘fad’ diets e.g. cabbage soup diet or Atkins diet.

Eat a CONSISTENT amount of vegetables high or moderate in vitamin K content

Green leafy vegetable Amount Vitamin K (mcg)
Kale Raw 1 cup chopped 810
Kale cooked ½ cup 561
Spinach cooked ½ cup 478
Dandelion greens raw 1 cup chopped 428
Spring greens/ Collards cooked ½ cup 442
Beet greens cooked ½ cup 348
Swiss Chard raw 1 cup 315
Swiss chard cooked ½ cup 303
Dandelion greens cooked ½ cup 290
Turnip greens cooked ½ cup 280
Parsley raw ¼ cup (16 sprigs) 260
Mustard greens cooked ½ cup 222
Collards, raw 1 cup chopped 194
Broccoli, raw 1 cup 176
Spinach, raw 1 cup 153
Beet greens, raw 1 cup 152
Broccoli, cooked 1 cup 121
Endive and Escarole, raw 1 cup 122
Brussel sprouts, cooked 4 sprouts 108
Radicchio, raw 1 cup 102
Lettuce dark green leaf, raw 1 cup 103
Cabbage, cooked ½ cup chopped 90
Lettuce, romaine, raw 1 cup 61
Lettuce, butterhead, raw 1 cup 60
Cabbage white, raw ½ cup chopped 47
Asparagus, cooked ½ cup 47
Spring onions/ Scallions 2 ea 42


Other high vitamin K foods

Food Amount Vitamin K (mcg)
Soya bean oil ½ cup 110
Soya bean oil 1 tablespoon 16.5
Rapeseed/ Canola oil ½ cup 95
Rapeseed/ Canola oil 1 tablespoon 14.2
Olive oil ½ cup 48
Olive oil 1 tablespoon 7
Mayonnaise ½ cup 28
Mayonnaise 1 tablespoon 4.2
Margarine ½ cup 56
Margarine 1 teaspoon 3

Healthy low vitamin K vegetables

It is important to eat a wide variety of fruit and vegetables. The following vegetables are low in vitamin K. One serving is ½ cup or 3-4 dessertspoons of cooked vegetables. Eat at least 4 servings of low Vitamin K vegetables and fruit per day to meet healthy guidelines.








Green beans

Green peas




Pumpkin/Butternut Squash


White Onions


Sweet potato


Turnip, flesh

Water chestnuts

Appointments for the 4th Practice Warfarin Clinic are available every day Monday to Friday from 8am to 1pm. Please phone 022-52944 to make an appointment.