OBJECTIVES:The purpose of this study was to determine whether performing the test bolus (TB) of computed tomography coronary angiography (CTCA) and computed tomography pulmonary angiography (CTPA) at 80 kVp reduces dose without compromising diagnostic quality. METHODS:An 80 kVp TB protocol for CTCA and CTPA was retrospectively compared to standard TB protocol (non-obese: 100 kVp, obese: 120 kVp). CT angiogram parameters were unchanged between cohorts. Thirty-seven consecutive 80 kVp TB CTCA images were compared to 53 standard CTCA images. Fifty consecutive CTPAs from each protocol were analysed. Diagnostic quality of the CT angiogram was assessed by: mean attenuation, signal-to-noise ratio (SNR) in the ascending aorta (AA) in CTCA and in the main pulmonary artery (MPA) in CTPA, diagnostic rate, and number of repeated monitoring scans. Mean effective dose was estimated using the dose-length product. RESULTS:Mean TB effective doses were significantly lower (P < 0.0001) for 80 kVp scans compared to the standard in non-obese CTCA (0.15 ± 0.04 mSv Vs 0.33 ± 0.09 mSv), obese CTCA (0.17 ± 0.06 mSv Vs 0.57 ± 0.12 mSv), and CTPA patients (0.07 ± 0.03 mSv Vs 0.15 ± 0.06 mSv). No difference was demonstrated in mean attenuation, SNR (AA), SNR (MPA), diagnostic rates, or number of repeated monitoring scans between protocols. CONCLUSIONS:Routinely performing TB at 80 kVp, regardless of body habitus, in CTCA and CTPA results in a small but significant dose reduction, without compromising CT angiogram diagnostic quality. KEY POINTS:• CT coronary angiography is performed to exclude the presence of significant coronary atherosclerosis. • CT pulmonary angiography is performed to diagnose pulmonary thromboembolism. • This retrospective study showed dose reduction by performing test bolus at 80 kVp. • Diagnosis can be made with reduced exposure to ionising radiation.