CT Calcium Score Cut-offs for Severe Aortic Stenosis
The validated sex-specific CT calcium score thresholds for diagnosing severe AS are ≥2000 Agatston units in men and ≥1200 Agatston units in women, with higher thresholds of ≥3000 Agatston units in men and ≥1600 Agatston units in women indicating very likely severe AS. 1
Primary Diagnostic Thresholds
The most widely validated and clinically implemented cut-offs are:
- Men: ≥2000 Agatston units indicates severe AS is likely 1, 2
- Women: ≥1200 Agatston units indicates severe AS is likely 1, 2
These thresholds have been confirmed across multiple international centers with excellent discrimination (C statistic: 0.92 in women, 0.89 in men) 2. The optimal thresholds identified in the largest multicenter cohort (1377 AU for women and 2062 AU for men) were nearly identical to previously established values 2.
Higher Certainty Thresholds
For greater diagnostic certainty:
- Men: ≥3000 Agatston units indicates severe AS is very likely 1
- Women: ≥1600 Agatston units indicates severe AS is very likely 1
Clinical Context for CT Calcium Scoring
CT calcium scoring should be reserved for specific clinical scenarios where echocardiography yields conflicting or uncertain data, not for routine screening 1. The primary indications include:
- Low-flow, low-gradient AS with preserved LVEF (AVA <1.0 cm², mean gradient <40 mmHg, LVEF ≥50%, stroke volume index <35 mL/m²) 1
- Low-flow, low-gradient AS with reduced LVEF where dobutamine stress echo is inconclusive 3, 1
- Normal-flow, low-gradient AS (AVA <1.0 cm², mean gradient <40 mmHg, stroke volume index ≥35 mL/m²) when clinical suspicion remains high 1
Prognostic Implications
Beyond diagnosis, calcium scores predict clinical outcomes:
- Scores above sex-specific thresholds independently predict aortic valve replacement and death (hazard ratio 3.90,95% CI 2.19-6.78) after adjusting for age, sex, peak velocity, and valve area 2
- In low-flow, low-gradient AS with reduced EF, median calcium scores of 2027 AU or higher predict increased mortality 4
- Higher calcium scores predict rapid stenosis progression and cardiac events, making them useful for risk stratification in asymptomatic patients 1, 5
Critical Caveats
High calcium scores confirm severe AS and low scores exclude it, but intermediate scores (between the thresholds) remain diagnostically uncertain 1. In these cases:
- Integrate calcium scores with clinical symptoms, valve morphology, and LV function 1
- Consider that elderly patients with typical symptoms and LV hypertrophy are more likely to have true-severe AS 1
- Mean gradients of 30-40 mmHg support severe AS diagnosis even with intermediate calcium scores 1
Special Population Considerations
In patients with discordant echocardiographic grading, only 36-55% of those classified as severe low-gradient AS meet calcium score criteria for severe AS 6. This heterogeneity indicates that calcium scoring can differentiate true-severe from pseudo-severe AS in this population, though the prognostic implications are less pronounced than in patients with concordant AS grading 6.
The benefit of aortic valve replacement is more pronounced in patients with higher calcium scores, particularly in low-flow, low-gradient AS where surgery improves survival primarily in those with scores above the median 4.