Predicting risk with oral anticoagulants

Key points

Safe and effective anticoagulation for stroke prevention in patients with non-valvular atrial fibrillation (NVAF) relies on balancing the benefits of blood clot prevention with the risks of bleeding.
Clinical risk scores can help with the initial decision on whether to prescribe an anticoagulant for a patient or not.
The CHA₂DS₂-VASc and HAS-BLED scores are well established for evaluating stroke risk for patients with atrial fibrillation (AF) and bleeding risk, respectively.
Oral anticoagulation is recommended for patients with a CHA₂DS₂-VASc score of ≥ 2 (men) or ≥ 3 (women).
A HAS-BLED score of ≥ 3 indicates a high risk of bleeding – regular review and treatment of modifiable bleeding risk factors is recommended for these patients, rather than avoidance of oral anticoagulation.
Some patients may accept a higher risk of bleeding, knowing that they are avoiding a stroke.

Balancing stroke and bleeding risk

The four oral anticoagulants listed on the Pharmaceutical Benefits Scheme (PBS) are warfarin, and three non-vitamin K antagonist oral anticoagulants: apixaban (Eliquis), dabigatran (Pradaxa) and rivaroxaban (Xarelto).^1-4

Of these, the non-vitamin K antagonists are Authority Required (Streamlined) for prevention of stroke or systemic embolism in a patient with non-valvular atrial fibrillation (NVAF) and one or more risk factors for developing stroke or systemic embolism.

Safe and effective treatment relies on balancing the benefits of blood clot prevention with the risks of bleeding – whichever anticoagulant is selected as the most appropriate medicine for an individual patient.

Clinical risk scores to stratify patients according to their stroke or bleeding risk can help with the initial decision on whether to prescribe an anticoagulant for a patient or not, and help identify modifiable risk factors for bleeding.⁵

A number of risk factors can be used to estimate stroke risk, several different bleeding risk scores have been developed, and stroke and bleeding risk factors can overlap.⁵

The CHA₂DS₂-VASc and HAS-BLED scores are well established for stroke risk in patients with AF and bleeding risk, respectively, and are recommended in current AF guidelines.^5-7

Predicting stroke risk

Guidelines recommend the CHA₂DS₂-VASc score for the prediction of stroke risk in patients with NVAF (see Table 1).^5-7

The CHA₂DS₂-VASc score was developed to overcome limitations of the simpler CHADS₂ score, including the grouping together of patients with different levels of risk and underestimation of stroke risk.⁸It has been validated in numerous AF populations.⁸

Using the CHA₂DS₂-VASc score:^5-7

Score ≥ 2 (men) or ≥ 3 (women) = Oral anticoagulation is recommended
Score 1 (men) or 2 (women) = Oral anticoagulation can be considered, based on individual patient characteristics and preferences
Score 0 (no clinical risk factors) = No anticoagulation (or antiplatelet medicine) is required.

When interpreting results, the relative weighting of individual risk factors and patient preferences should still be considered, especially in patients with only a single risk factor (besides female sex).^5-7

For example, advancing age is associated with other stroke risk factors (such as heart failure), whereas female sex alone does not increase stroke risk in the absence of other risk factors.^5,6

Note that, due to limited evidence, antiplatelet medicines are not recommend for stroke prevention in AF, irrespective of stroke risk.⁵

Table 1: CHA₂DS₂-VASc clinical score for risk of stroke, transient ischaemic attach or systemic embolism^5-7
Risk factor	Score
Congestive heart failure Signs/symptoms of heart failure or objective evidence of reduced left-ventricular ejection fraction	1
Hypertension Resting blood pressure > 140/90 mmHg on ≥ 2 occasions, or current antihypertensive treatment	1
Age ≥ 75 years	2
Diabetes mellitus Fasting glucose > 7 mmol/L or treatment with oral hypoglycaemic agent and/or insulin	1
Previous stroke, transient ischaemic attack, or thromboembolism	2
Vascular disease Previous myocardial infarction, peripheral artery disease, or aortic plaque	1
Age 65–74 years	1
Sex category (female)	1

Predicting bleeding risk

Guidelines recommend the HAS-BLED score for the prediction of bleeding risk in patients with NVAF (see Table 2).^5-7

Using the HAS-BLED score^5,7,8

Score ≥ 3 = High risk of bleeding, for which caution and regular review is recommended.

A high score identifies patients who may be at high risk of bleeding, as well as potentially modifiable bleeding risk factors. A high score does not necessarily indicate that anticoagulant medicines should be avoided.^5,8

Table 2: HAS-BLED clinical score for risk of bleeding⁵
Risk factor	Score
Hypertension Systolic blood pressure > 160 mmHg	1
Abnormal kidney and/or liver function (1 point each) Chronic dialysis, renal transplantation or serum creatinine ≥ 200 micromol/L Chronic liver disease (eg, cirrhosis) or biochemical evidence of significant hepatic derangement	1 or 2
Stroke	1
Bleeding tendency or predisposition Bleeding history or anaemia	1
Labile international normalised ratio (INR) Time in therapeutic range < 60%	1
Elderly Age > 65 years	1
Drugs and/or alcohol (1 point each) Concomitant antiplatelet or non-steroidal anti-inflammatory drugs, or excess alcohol	1 or 2

Treat modifiable bleeding risk factors

In patients with a high bleeding risk, all bleeding risk factors should be identified and modifiable risk factors should be addressed.^5,6,7

Based on risk factors included in the HAS-BLED score, and other bleeding risk clinical scores (HEMORR₂HAGES, ATRIA, ORBIT, ABC), modifiable bleeding risk factors include:⁵

hypertension (especially when systolic blood pressure is > 160 mmHg)
labile INR or time in therapeutic range < 60% (in patients taking warfarin)
medicines that may predispose to bleeding (such as antiplatelet medicines or NSAIDs)
excessive alcohol consumption (typically ≥ 8 drinks/week).

Potentially modifiable bleeding risk factors include:⁵

anaemia
impaired kidney function
reduced platelet count or function.

Non-modifiable bleeding risk factors include:⁵

age > 65 years, or ≥ 75 years
history of major bleeding
previous stroke
dialysis-dependent kidney disease or kidney transplant
cirrhotic liver disease
malignancy
genetic factors.

Overall, stroke and bleeding risk should be assessed on a patient-by-patient basis when considering an oral anticoagulant, but assessment of bleeding and other risks should continue throughout treatment.^{9 -13}

All patients should be educated about the benefits and risks associated with anticoagulant medicines, so they can contribute to management decisions.

For example, some patients may accept a higher risk of bleeding, knowing that they are avoiding a stroke.

NPS MedicineWise oral anticoagulation resources

Take a look at the Resources section of the Anticoagulants page for:

Predicting risk with oral anticoagulants

Key points

Balancing stroke and bleeding risk

Predicting stroke risk

Using the CHA₂DS₂-VASc score:^5-7

Predicting bleeding risk

Using the HAS-BLED score^5,7,8

Treat modifiable bleeding risk factors

NPS MedicineWise oral anticoagulation resources

References

Date reviewed: 20 January 2021

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Predicting risk with oral anticoagulants

Key points

Balancing stroke and bleeding risk

Predicting stroke risk

Using the CHA2DS2-VASc score:5-7

Predicting bleeding risk

Using the HAS-BLED score5,7,8

Treat modifiable bleeding risk factors

NPS MedicineWise oral anticoagulation resources

References

Date reviewed: 20 January 2021

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Using the CHA₂DS₂-VASc score:^5-7

Using the HAS-BLED score^5,7,8