Comparison of Prehospital and Emergency Department Performance of the Assessment of Blood Consumption Score

The Assessment of Blood Consumption (ABC) score is used to identify patients requiring activation of a massive transfusion protocol (MTP) but relies on ultrasonography. Identifying these patients prior to hospital arrival could expedite MTP activation; however, the validity of a prehospital ABC score has not been established, especially as ultrasonography is rarely available in that setting. This study aimed to compare the performance of a prehospital ABC score (without ultrasonography) with that of the ABC score calculated on arrival to the emergency department (ED) (with ultrasonography).

We conducted a single-center retrospective study at the Hôpital du Sacré-Cœur de Montréal, a tertiary trauma center (65,000 annual ED visits, including 3,000 trauma) in Canada. Patients aged ≥16 years presenting between July 2024 and July 2025 following severe trauma (e.g., trauma team activation, intensive care unit admission) were included. Patients transferred from another hospital were excluded. The primary outcome was the need for MTP, defined as transfusion of ≥6 units of packed red blood cells within 4 hours. Sensitivity and specificity were calculated for each ABC threshold, and receiver operating characteristic (ROC) curves were generated. Predictive performance was compared using a paired z-test. Assuming an AUC difference of 0.30 (0.90 vs 0.60), a sample of 200 patients would provide >80% power at a two-sided α of 0.05, assuming a 5% MTP rate and within-subject correlations of 0.50.

Among 547 potentially eligible patients, 223 were included (mean age: 48 years; male: 74%; penetrating trauma: 22%), of whom 12 (5%) required MTP. In the prehospital setting, an ABC score ≥1 yielded a sensitivity of 100% (95%CI 72–100) and a specificity of 50% (95%CI 42–57), while an ABC score ≥2 yielded a sensitivity of 55% (95%CI 23–83) and a specificity of 90% (95%CI 84–94). In the ED, an ABC score ≥2 demonstrated a sensitivity of 100% (95%CI 69–100) and a specificity of 93% (95%CI 88–96). The area under the ROC curve was higher for the ED ABC score compared with the prehospital score (0.98 [95%CI 0.97–1.00] vs 0.85 [95%CI 0.75–0.94], p=0.004).

The prehospital ABC score demonstrates good performance for early prediction of MTP activation, although it remains less accurate than the ED ABC score. A prehospital threshold ≥1 appears as sensitive but less specific than an ED threshold ≥2.