Warfarin Bleeding Risk Score

Variables considered

Long term anticoagulation therapy, such as that with Warfarin, may lead to an increase in haemorrhage risk. This risk can also be heightened by personal factors.

The Warfarin bleeding risk score calculator is based on the Outpatient Bleeding Risk Index and consists of the following factors:

■ Age – patients aged 65 or more are more predisposed to bleeding;

■ Personal history of cerebrovascular accident (CVA);

■ Personal history of gastrointestinal bleeding;

■ Any of the following present: recent MI, anemia with HCT <30%, Creat >1.5,

Each of th above factors are given 1 point when present. Therefore, the score ranges from 0 to 4. The potential bleeding risk at 3 and 12 months can be found in the table below:

About the study

The original study was conducted by Beyth et al. in 1998 and consisted of a derivation cohort of 556 patients and a validation cohort of 264 patients.

Major bleeding occurred in 87 of 820 outpatients. In the validation cohort, the index predicted major bleeding with the following cumulative incidence at 48 months:

■ 3% in low-risk patients;

■ 12% in intermediate risk patients;

■ 53% in high-risk patients.

It was found that 17 of the 18 episodes of bleeding in high risk patients were preventable, by avoidance of over-anticoagulation and nonsteroidal anti-inflammatory agents.

During one validation study, the Outpatient Bleeding Risk Index was found to discriminate between low- and moderate risk patients and could potentially guide decisions regarding optimal duration of anticoagulant therapy with Warfarin.

Warfarin and INR monitoring

Long term anticoagulation is the chosen therapeutic approach in preventing recurrent thrombosis that occurs in conditions such as deep venous thrombosis or pulmonary embolism.

However, anticoagulation drugs pose the risk of serious bleeding because they decrease the action of clotting factors (especially vitamin K dependent factors), thus their prescription needs to take in consideration other patient risk factors and comorbidities.

Prothrombin time (protime) is a test that measures the time in which the blood clots. This is reported as the International Normalized Ratio (INR). The longer the blood takes to clot, the higher the PT and the INR.

During anticoagulation therapy, INR values are to be monitored at least once or twice a month in the first three months (when there is higher bleeding risk) and at least four to six weekly after three months.

The target INR is between 2 and 3, which means that blood clots are prevented and the coagulation function is not completely impaired, as to lead to bleeding. However, the target range is achieved in around 55% of cases during treatment because INR levels show intra patient variability.

When the patient is under-anticoagulated the INR values are below the target range, thus there is risk of blood clotting.

When the patient is over-anticoagulated, the INR values are above the target range and there is risk of haemorrhage.

INR changes may occur in stable patients due to drug interactions, lack of compliance to therapy, not keeping a medication schedule or due to stress causes and changes in physical activity or diet.

Original source

Beyth RJ, Quinn LM, Landefeld CS. Prospective evaluation of an index for predicting the risk of major bleeding in outpatients treated with warfarin. Am J Med. 1998; 105(2):91-9.

Validation

Wells PS, Forgie MA, Simms M, Greene A, Touchie D, Lewis G, Anderson J, Rodger MA. The outpatient bleeding risk index: validation of a tool for predicting bleeding rates in patients treated for deep venous thrombosis and pulmonary embolism. Arch Intern Med. 2003; 163(8):917-20.