Massive hemorrhage is a major cause of early death in trauma patients. A vast majority of US trauma centers haves established Massive Transfusion Protocols (MTP) in order to facilitate early and aggressive balanced resuscitation. Though some institutions have created initiation policies to activate MTP, others rely on subjective clinical judgment based on initial vital signs for activation. However, research shows that a single set of vital signs is a poor predictor of need for MTP. As a result, various scoring systems were developed to predict need for massive transfusion in traumatically injured patients. Assessments of Blood Consumption (ABC) score and Shock Index (SI) have been shown to be reliable predictors for MTP activation. No study has directly compared ABC Score and SI in determining which is a better predictor for MTP activation.

Clinical Question

Which scoring system, ABC Score or Shock Index, is a better predictor of need for early activation of MTP? (MTP defined as a need for 10+ units of pRBCs within 24 hours of emergency department arrival)


Adults aged 18 years and older who were trauma activations between January 1, 2009 and December 31, 2013 at a single urban Level 1 Trauma Center.


Applications of ABC Score and Shock Index
ABC Score: a score of ≥ 2 was defined as the cut-off to predict need for MTP
– Penetrating mechanism
– Positive Focused Assessment of Sonography in Trauma (FAST)
– ED SBP <90 mmHg, - ED HR >120 beats per minute
Shock Index (SI): a score of ≥ 1 was defined as the cut-off to predict need for MTP. SI was calculated as initial HR divided by initial SBP


Performance characteristics (sensitivity, specific, ROC Curve) of ABC score versus SI


Retrospective Cohort Study from an Existing Trauma Registry


Patients with Traumatic Brain Injury (TBI); patients with missing data (ie. SBP, HR, or FAST exam)

Primary Results

  • 6460 patients screened for enrollment
    • 336 patients excluded due to lack of data (SBP, HR, Blood Product Data)
    • 5480 patients excluded because they did not receive FAST examinations in the ED
  • 644 patients included based on inclusion criteria
      • 34 patients needing MTP
      • 5% MTP Activation

Critical Findings (95% CI)

AUROC Sensitivity Specificity (+) LR* (-) LR*
ABC Score ABC > 2: 0.74 47.0% 89.9% 4.65 0.59
Shock Index SI > 1: 0.83 67.7% 81.3% 3.62 0.40

AUROC: Area Under Receiver Operating Characteristic Curve

  • The area under the ROC curve (AUC) is a measure of how well a parameter can distinguish between two diagnostic groups (diseased/normal).
  • AUROC Values are a Reflection of Diagnostic Accuracy1:
    • 0.90 – 1.0 = Excellent
    • 0.80 – 0.90 = Good
    • 0.70 – 0.80 = Fair
    • 0.60 – 0.70 = Poor
    • 0.50 – 0.60 = Fail

Wikipedia: Likelihood Ratios


  • Study asked a simple, clinically relevant question
  • Used a simple cutoff value for SI (SI > 1.0) in analysis (pragmatic to clinical scenarios)


  • Study is retrospective in nature and restricted to a specific population within a single urban trauma center
  • 5480 patients were excluded (~85% of initial enrollment) because they did not receive a FAST examination in the ER
  • There is no consideration of medications that may affect vital signs (i.e. beta blockers) for either of these scoring systems
  • The FAST examination, which is a component of the ABC score, is operator dependent and thus accuracy depends on technical skill

Author's Conclusions

“ABC score and Shock Index can both be used to predict need for massive transfusion in trauma patients, however SI is more sensitive and requires less technical skill than ABC score.”

Our Conclusions

In this single center retrospective study, SI appears to be a more accurate predictor and requires less technical skill than ABC Score in determining a need to activate MTP.

Potential Impact To Current Practice

Providers should consider using an objective score to aid in making the decision to activate MTP. SI may be a more useful decision aid than the ABC score and is simpler to use.

Bottom Line

While shock index is simple to calculate, and can be used in the pre-hospital and performed slightly better than the ABC score, further research is needed to define the best approach. Additionally, this study did not compare either tool to provider evaluation and clinical gestalt should not be ignored when deciding if and when to activate MTP.