Warfarin Therapy Calculator

Stratifies major bleeding risk in patients under anticoagulation therapy with Warfarin.

In the text below the form you can read more about bleeding risk factors and possible Warfarin side effects.

The Warfarin therapy calculator uses patient age, gender and whether malignancy is present, to estimate the risk for major bleeding occurring, during anticoagulation therapy.

There are three bleeding risk categories:

Score Risk of major bleeding Risk of any bleeding complications
0 0 – 1% 0 – 4%
1.3 – 3 1 – 2% 6 – 8%
3.1 – 5.1 7 – 14% 17 – 26%







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Steps on how to print your input & results:

1. Fill in the calculator/tool with your values and/or your answer choices and press Calculate.

2. Then you can click on the Print button to open a PDF in a separate window with the inputs and results. You can further save the PDF or print it.

Please note that once you have closed the PDF you need to click on the Calculate button before you try opening it again, otherwise the input and/or results may not appear in the pdf.


The bleeding risk scoring method explained

Patients under anticoagulation therapy with Warfarin are at risk of bleeding, if overmedicated or at risk of blood clots if undermedicated.

There are several risk factors that contribute to bleeding risk, three of which are accounted for in the above calculator:

■ Patient age – the age cut off for increased risk is placed at 60 years old;

■ Patient gender – women are considered to have a higher bleeding risk compared to men;

■ Malignancy – presence or absence of cancer.

Each of the three components is weighted differently (number of points) depending on the risk contribution.

The score obtained by summing the results is correlated with a percentage range of major bleeding risk and bleeding complications risk.

Score Risk of major bleeding Risk of any bleeding complications
0 0 – 1% 0 – 4%
1.3 – 3 1 – 2% 6 – 8%
3.1 – 5.1 7 – 14% 17 – 26%

Patients under therapy with other medication aside from Warfarin, such as NSAIDs, hypertensive patients (with systolic blood pressure higher than 160 mmHg), patients with labile INR or patients with personal history of stroke are at higher risk of major bleeding.


Warfarin side effects

All anticoagulant therapies have as major complication haemorrhage. The bleeding risk is higher during the first 3 months of treatment and decreases after this period.

It is important that patients know that they need to report any accidents, bruising or signs of bleeding because excessive, diffuse bleeding can occur in any area of the body.

Signs of bleeding to be reported include bleeding from gums, epistaxis or blood in urine or stool.

The table below summarizes possible side effects of Warfarin therapy:

Prolonged bleeding after cuts Chest pain Headaches, dizziness
Nausea, stomach upset, diarrhea Difficulty breathing Confusion
Vomiting blood Nosebleed Prolonged tiredness or weakness
Fever not associated with infection Dark urine Bruising, swelling
Blurred vision Dark colored stool Excessive menstrual bleeding

There are several counterindications for Warfarin therapy, for example in patients with protein C deficiency, a rare inherited clotting disorder, Warfarin may lead to skin necrosis or gangrene in the first days after introduction of anticoagulation therapy.

Other counterindications include:

■ Patients with high blood pressure;

■ Recent surgery or stroke;

■ Impaired liver or kidney function;

■ Pregnancy or breastfeeding.



1. Kuijer PM, Hutten BA, Prins MH, Büller HR. Prediction of the risk of bleeding during anticoagulant treatment for venous thromboembolism. Arch Intern Med. 1999;159(5):457-60.

2. Whitley HP, Fermo JD, Chumney ECG, Brzezinski WA. Effect of patient-specific factors on weekly warfarin dose. Ther Clin Risk Manag. 2007; 3(3): 499–504.

3. Kuruvilla M, Gurk-Turner C. A review of warfarin dosing and monitoring. Proc (Bayl Univ Med Cent). 2001; 14(3): 305–306.

Specialty: Pharmacology

Objective: Evaluation

Type: Calculator

No. Of Variables: 3

Article By: Denise Nedea

Published On: May 30, 2017

Last Checked: May 30, 2017

Next Review: May 30, 2023