Warfarin Therapy Calculator

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.

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:

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.

References

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.