This Warfarin therapy bleeding risk calculator evaluates risk of major bleeding and any related complications in patients treated with this anticoagulant. The text below the form features more information on the risk percentages and on the side effects of Warfarin.







How does this warfarin therapy bleeding risk calculator work?

This health tool determines risk of major and any bleeding complications in patients considered for warfarin therapy based on age, gender and presence of malignancy.

The original study aimed at constructing and validating a bleeding risk prediction score that could be easily applied before the institution of anticoagulant therapy. It involved a cohort of patients suffering from diagnosed venous thromboembolism.

The warfarin therapy bleeding risk calculator awards different weights to each of the three components and computes bleeding risk percentages in concordance with the guidelines in the study cited below at reference #1:

■ Age – patient data with the cut off for increased risk placed at 60 years old;

■ Gender – females considered to have increased bleeding risk compared to males;

■ Malignancy – presence or absence of cancer.

The following table presents bleeding risks in the three 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%

Other individual bleeding risk factors include:

■ Labile INR;

■ Therapy with other medication, especially NSAIDs;

■ Hypertension with systolic blood pressure higher than 160 mmHg;

■ Personal history of stroke;

■ Abnormal renal or liver function.

Warfarin side effects

The major complication of most anticoagulant therapies including Warfarin, is bleeding. The risk varies with the different phases of the treatment, being higher in the first few weeks after the start of the therapy.

Excessive bleeding can occur in any area of the body, therefore patients are advised to report any accidents, bruising or signs of bleeding.

Signs of bleeding include bleeding from gums, vomiting blood, epistaxis and blood in urine or stool.

Counter indications of warfarin include the following conditions that should be brought to the doctor’s attention before treatment:

■ High blood pressure;

■ Under treatment with other medicines;

■ Allergic reactions to medicines;

■ Problems with liver or kidney function;

■ Diagnosed conditions such as stomach ulcer;

■ Recent surgery or stroke;

■ Pregnancy, breastfeeding;

■ Recent, unhealed cuts and wounds.

Risk of bleeding and the balance between proper anticoagulation and under or over coagulation is maintained by monitoring prothrombin time and determining the INR (International Normalized Ratio).

Possible side effects of Warfarin include:

■ Headaches, dizziness;

■ Nausea, stomach upset, diarrhea;

■ Prolonged tiredness or weakness;

■ Fever associated with infection;

■ Blurred vision;

■ Difficulty breathing;

■ Chest pain;

■ Confusion;

■ Vomiting blood;

■ Nosebleed;

■ Bruising, swelling;

■ Dark urine;

■ Dark colored stool;

■ Excessive menstrual bleeding;

■ Prolonged bleeding after cuts.

In patients with protein C deficiency, a rare inherited clotting disorder, warfarin side effects may lead to skin necrosis or gangrene in the first days after introduction of therapy.


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

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

3) Baglin TP et al. (2006) British Committee for Standards in Haematology - Guidelines on oral anticoagulation (warfarin): third edition - 2005 update. British Journal of Haematology; 132 (3): 277-285.

4) Piatkov I, Rochester C, Jones T, Boyages S. (2010) Warfarin Toxicity and Individual Variability—Clinical Case. Toxins (Basel); 2(11): 2584–2592.

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

29 May, 2016