New risk equations can help determine the need for a first coronary artery calcium (CAC) scan in young adults to identify those most at risk for premature atherosclerosis, researchers say.

“To our knowledge this is the first time to derive a clinical risk equation for the initial conversion from CAC 0, which can be used actually to guide the timing of CAC testing in young adults,” Omar Dzaye, MD, MPH, PhD, Johns Hopkins University School of Medicine, Baltimore, said in an interview.

CAC is an independent predictor of adverse atherosclerotic cardiovascular disease (ASCVD) but routine screening is not recommended in low-risk groups. US guidelines say CAC testing may be considered (class IIa) for risk stratification in adults 40 to 75 years at intermediate risk (estimated 10-year ASCVD risk 7.5% to 20%) when the decision to start preventive therapies is unclear.

The new sex-specific risk equations were derived from 22,346 adults 30 to 50 years of age who underwent CAC testing between 1991 and 2010 for ASCVD risk prediction at four high-volume centers in the CAC Consortium. The average age was 43.5 years, 25% were women, and 12.3% were non-White.

The participants were free of clinical ASCVD or CV symptoms at the time of scanning, but had underlying traditional ASCVD risk factors (dyslipidemia in 49.6%, hypertension in 20.0%, active smokers 11.0%, and diabetes in 4.0%), an intermediate 10-year ASCVD risk (2.6%), and/or a significant family history of CHD (49.3%).

As reported in the Journal of the American College of Cardiology, 92.7% of participants had a low 10-year ASCVD risk below 5%, but 34.4% had CAC scores above 0 (median, 20 Agatston units).

Assuming a 25% testing yield (number needed to scan equals four to detect one CAC score above 0), the optimal age for a first scan in young men without risk factors was 42.3 years, and for women it was 57.6 years.

Young adults with one or more risk factors, however, would convert to CAC above 0 at least 3.3 years earlier on average. Diabetes had the strongest influence on the probability of conversion, with men and women predicted to develop incident CAC a respective 5.5 years and 7.3 years earlier on average.

The findings build on previous observations by the team showing that diabetes confers a 40% reduction in the so-called “warranty period” of a CAC score of 0, Dzaye noted. The National Lipid Association 2020 statement on CAC scoringalso suggests it’s reasonable to obtain a CAC scan in people with diabetes aged 30 to 39 years.

“The predicted utility of CAC for ASCVD outcomes is similar in type 1 and type 2 diabetes; however, individuals with type 1 diabetes may actually develop CAC as young as 17 years of age,” he said. “Therefore, definitely, CAC studies in this population are required.”

In contrast, hypertension, dyslipidemia, active smoking, and a family history of CHD were individually associated with the development of CAC 3.3 to 4.3 years earlier. In general, the time to premature CAC was longer for women than for men with a given risk-factor profile.