MESA Risk Score (with optional CAC)

About MESA Risk Score (with optional CAC)

MESA Risk Score

The MESA Risk Score, published by McClelland and colleagues in JAMA in 2015, was developed from the Multi-Ethnic Study of Atherosclerosis, a landmark NIH-funded cohort of 6,814 men and women aged 45-84 from four U.S. racial/ethnic groups (white, Black, Hispanic, and Chinese American). Unlike the Pooled Cohort Equations (which were derived partly from MESA data but excluded CAC), the MESA Risk Score explicitly incorporates coronary artery calcium (CAC), which dramatically improves risk discrimination and reclassification in the intermediate-risk range.

What the calculator measures

The MESA Risk Score estimates 10-year risk of hard coronary heart disease events (MI, angina followed by revascularization, CHD death, resuscitated cardiac arrest) and, in some implementations, total ASCVD events. The unique value of the MESA score is that it produces two parallel estimates, one without CAC and one with CAC, allowing clinicians to see exactly how much risk reclassification the CAC scan provides. For intermediate-risk patients, this can mean the difference between starting a statin and deferring therapy.

How the formula works

The MESA Risk Score is a Cox proportional hazards model with log-transformed age, cholesterol, HDL, SBP, and (optionally) log(CAC+1). It includes race/ethnicity indicators for Chinese, Black, and Hispanic (with white as reference), binary indicators for current smoking, diabetes, antihypertensive treatment, and family history of CVD. The full coefficients are extensive (the published online calculator at mesa-nhlbi.org implements all of them). The simplified JavaScript implementation here uses representative coefficient values; for clinical decisions, the official MESA Risk Calculator is the validated tool. The CAC coefficient is the most powerful single risk predictor in the model. A CAC of 0 typically reduces estimated risk by 30-50% relative to the no-CAC model, while a CAC >300 typically increases risk by 2-4 fold. The CAC effect is roughly log-linear, meaning each doubling of CAC carries a similar incremental risk.

Interpretation

The risk tiers mirror those of the ASCVD PCE: <5% low, 5-10% borderline, 10-20% intermediate, >20% high. The 2018 ACC/AHA cholesterol guideline explicitly endorses CAC scoring as the preferred tie-breaker for intermediate-risk patients: a CAC of 0 favors deferring statins (unless diabetes, family history of premature CHD, or cigarette smoking is present), while a CAC ≥100 or ≥75th percentile for age/sex/race favors statin initiation.

Clinical use

The MESA Risk Score is most useful in two scenarios. First, in intermediate-risk patients (ASCVD 7.5-20%) for whom the statin decision is uncertain. CAC scoring reclassifies approximately 40-50% of these patients, half downward (CAC=0, defer statins) and half upward (CAC≥100, initiate statins). Second, in patients younger than 50 or older than 79 (outside the PCE age range) for whom the PCE are not validated. MESA covers ages 45-84 and can provide a risk estimate when the PCE cannot.

Limitations

The MESA Risk Score was derived in a U.S. cohort and is most accurate in populations that resemble the MESA sample. It requires a CAC scan for full use, which adds cost (~$100-300 in the U.S.) and exposes the patient to a small dose of ionizing radiation (~1 mSv, roughly equivalent to 4 months of background radiation). CAC scoring is not universally available and may not be covered by insurance. The score does not include hs-CRP, Lp(a), or apoB, which are additional risk enhancers. The simplified JavaScript implementation here is approximate; for clinical decisions, the official MESA Risk Calculator should be used.

Comparison with ASCVD PCE

For patients with CAC=0, the MESA score typically gives risk estimates 30-50% lower than the ASCVD PCE because CAC=0 is a powerful negative predictor. For patients with CAC>300, the MESA score typically gives risk estimates 2-3 fold higher than the PCE. The two scores agree most closely in the absence of CAC data (in which case MESA-no-CAC is essentially a recalibrated ASCVD). The MESA score's strength is its explicit incorporation of CAC, which is the single most powerful predictor of coronary events available in primary prevention.

How to use the result

A MESA score of 12% (with CAC) means approximately 12 out of 100 people with similar risk factors and CAC will have a coronary event in the next decade. The CAC-augmented risk should be the primary driver of statin decisions in intermediate-risk patients. For patients reclassified from intermediate to low risk by CAC=0, the conversation can focus on lifestyle therapy and serial risk factor monitoring; for patients reclassified upward, statin therapy is indicated.