Will CAC Show Pulmonary Embolism?
No, a Coronary Artery Calcium (CAC) scan will not show pulmonary embolism and should never be used for this purpose.
Why CAC Cannot Detect PE
A CAC scan is a non-contrast CT examination specifically designed to quantify calcium deposits in the coronary arteries for cardiovascular risk stratification. It fundamentally cannot visualize pulmonary embolism for several critical reasons:
- No intravenous contrast is administered during CAC scanning, making it impossible to visualize filling defects in the pulmonary arteries that define PE 1
- The ACR Appropriateness Criteria explicitly state there is no relevant literature to support the use of CT chest without IV contrast to assess PE 1
- CAC scans are not rated as appropriate (rated 2/9 "usually not appropriate") for PE diagnosis by the American College of Radiology 2
The Correct Imaging for PE
CT pulmonary angiography (CTPA) with IV contrast is the first-line diagnostic test for suspected pulmonary embolism:
- CTPA has sensitivity of 96-99% and specificity of 96-99% for detecting PE, making it the definitive diagnostic test 3, 4
- Modern multidetector CTPA can detect emboli down to 2-3 mm in subsegmental arteries with extremely low false-negative rates 3
- CTPA provides excellent spatial resolution, detailed evaluation of vasculature and lung parenchyma, and can identify alternative diagnoses 1
Alternative Imaging When CTPA Is Contraindicated
If IV contrast cannot be administered (e.g., severe renal dysfunction or contrast allergy):
- Ventilation-perfusion (V/Q) scan is the preferred alternative with sensitivity of 96-97.4% and specificity of 90-95% 2
- Lower extremity duplex Doppler ultrasound can substitute by demonstrating deep vein thrombosis (rated 7/9 "usually appropriate"), though if negative, further studies to exclude PE are indicated 1, 2
- MR angiography has limited sensitivity for peripheral PE and is rated 2/9 "usually not appropriate" 2
Critical Pitfall to Avoid
Never rely on non-contrast CT imaging of any type—including CAC scans—for PE diagnosis, as this carries significant risk of missed diagnosis with potentially fatal consequences 2. The mortality risk of untreated PE far outweighs concerns about contrast administration in most clinical scenarios 2.