The CHADS₂ score and its updated version, the CHA₂DS₂-VASc score, are clinical prediction rules for estimating the risk of stroke in people with non-rheumatic atrial fibrillation (AF), a common and serious heart arrhythmia associated with thromboembolic stroke. Such a score is used to determine whether or not treatment is required with anticoagulation therapy or antiplatelet therapy,^[1] since AF can cause stasis of blood in the upper heart chambers, leading to the formation of a mural thrombus that can dislodge into the blood flow, reach the brain, cut off supply to the brain, and cause a stroke.

A high score corresponds to a greater risk of stroke, while a low score corresponds to a lower risk of stroke. The CHADS₂ score is simple and has been validated by many studies.^[2] In clinical use, the CHADS₂ score (pronounced "chads two") has been superseded by the CHA₂DS₂-VASc score ("chads vasc"^[3]), which gives a better stratification of low-risk patients.

The CHA₂DS₂-VASc score is a widely used medical tool used to guide physicians on blood thinning treatment to prevent stroke in people with non-valvular atrial fibrillation (AF).^[4][5]

The CHADS₂ score does not include some common stroke risk factors, and its various pros/cons have been carefully discussed.^[6] Adding together the points that correspond to the conditions that are present results in the CHADS₂ score, that is used to estimate stroke risk.

To complement the CHADS₂ score, by the inclusion of additional 'stroke risk modifier' risk factors, the CHA₂DS₂-VASc-score has been proposed.^[8]

In clinical use, the CHADS₂ score has been superseded by the CHA₂DS₂-VASc score, which gives a better stratification of low-risk patients. The CHADS₂ score has been outperformed by the CHA₂DS₂-VASc in multiple patient groups including patients with AF who are receiving outpatient elective electrical cardioversion.^[9]

Thus, the CHA₂DS₂-VASc score is a refinement of CHADS₂^[8][10] score and extends the latter by including additional common stroke risk factors, that is, age 65–74, female gender and vascular disease.^[11] In the CHA₂DS₂-VASc score, 'age 75 and above' also has extra weight, with 2 points.

The maximum CHADS₂ score is 6, whilst the maximum CHA₂DS₂-VASc score is 9 (not 10, as might be expected from simply adding up the columns; the maximum score for age is 2 points).

Major guidelines have used the above fixed annual stroke risk as a guideline of starting anticoagulant treatment; where the ischemic stroke risk of more than 1% to 2% should be an indication to start an anticoagulant therapy. However, actual risk of getting stroke varies according to sampling method and geographical regions, as well as use of appropriate study analysis methodology.^[13] A meta-analysis of various studies in 2015 shown that annual stroke risk is less than 1% in 13 of the 17 studies for CHA₂DS₂-VASc score of 1, 6 out of 15 studies reported risk of 1 to 2% and 5 out of 15 studies reported risk of more than 2% for CHA₂DS₂-VASc score of 2.^[14] Nevertheless, stroke rates vary by study setting (hospital vs community), population (trial vs general), ethnicity, etc. Some studies included in the metaanalysis include females with score 1 by virtue of gender (who are low risk), into the aggregate rates; others included do not account for followup anticoagulation use (thus lowering rates) and were analysed by excluding all patients ever started on anticoagulants ('conditioning on the future' error).^[15]

The CHA₂DS₂-VASc Score has shown increasing popularity over time while the CHADS₂ has shown decreasing popularity,^[16] which could "partly be related to introduction of guidelines recommending the use of the CHA₂DS₂-VASc score for stroke risk stratification".^[16] The predictive abilities of risk scores for ischemic stroke in patients with kidney function impairment is questionable: a large head-to-head external validation study demonstrated poor discrimination and calibration in patients with reduced kidney function.^[17]

The CHA₂DS₂-VASc score has been used in the 2012 and subsequent European Society of Cardiology guidelines for the management of atrial fibrillation.^{[18][19][20][21]} The 2014 American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society guidelines also recommend use of the CHA₂DS₂-VASc score.^[22]

The European Society of Cardiology (ESC),^[21] and National Institute for Health and Care Excellence (NICE)^[23] guidelines recommend that if the patient has a CHA₂DS₂-VASc score of 2 and above, oral anticoagulation therapy (OAC) with a vitamin K antagonist (VKA, e.g. warfarin with target INR of 2-3) or one of the direct oral anticoagulant drugs (DOACs, e.g. dabigatran, rivaroxaban, edoxaban, or apixaban) is recommended.

If the patient is 'low risk' using the CHA₂DS₂-VASc score (that is, 0 in males or 1 in females), no anticoagulant therapy is recommended.

In males with 1 stroke risk factor (that is, a CHA₂DS₂-VASc score=1), antithrombotic therapy with OAC may be considered, and people's values and preferences should be considered.^[24] Even a single stroke risk factor confers excess risk of stroke and mortality, with a positive net clinical benefit for stroke prevention with oral anticoagulation, when compared to no treatment or aspirin.^[25] As mentioned above, thromboembolic event rates differ according to various guideline treatment thresholds and methodological approaches.^[26]

The CHA₂DS₂-VASc score expanded from the CHADS2 score, first published in 2001.^[35]