Simple as ABC — and accurate, too

The assessment of blood consumption (ABC) score is a tool for identifying trauma patients who require massive transfusion — at least 10 units of blood in a 24-hour period.

The score is calculated by assigning one point to each of four unweighted parameters: heart rate greater than 120 bpm, systolic blood pressure less than 90 mm Hg, positive results on focused assessment with sonography for trauma (FAST) and penetrating mechanism of injury. A score of 2 or more indicates the need for transfusion.

Developed at Vanderbilt University and later validated in a multicenter trial, the ABC model is easy to use, quickly implemented — even, in some cases, before patients arrive in the trauma bay — and significantly more predictive than other systems. It also doesn't require blood tests or complicated mathematical calculations.

But although the advantages of ABC are clear, the original studies had limitations, says Martin D. Zielinski, M.D., of the Division of Trauma, Critical Care & General Surgery at Mayo Clinic in Rochester, Minn. He explains, "The ABC model was developed and validated in urban settings. Yet much of the United States is rural, with significant differences in pre-hospital care. In rural areas, response times are generally longer and transport times are often double those in urban areas. Communication between trauma centers and the field is more difficult, and there is less medical air support overall."

Dr. Zielinksi also points to procedural problems in the initial studies. "The developmental study excluded people who didn't receive blood, so observations involved only the most severely injured patients. And the validation study excluded interfacility transfers, which make up most trauma cases."

To help rectify these omissions, researchers performed a retrospective study of 373 people admitted to Saint Marys Hospital, one of Mayo Clinic's hospitals in Rochester, Minn., and a Level 1 trauma center, from 2008 to 2009. In this analysis, the ABC score was predictive of the need for transfusion in 89 percent of patients, nearly half of whom were interfacility transfers. Specificity was 85 percent, and over- and undertriage rates were just 13 and 11 percent respectively — well within the acceptable range.

Dr. Zielinski notes that the ABC score was even more predictive in Saint Marys' diverse population than in the original cohort.

Given the high marks the ABC model received in this study, Mayo Clinic now uses the system to activate its massive transfusion protocol and to counsel referring centers. The clinic is also working to implement ABC scoring in its catchment area.

"It's quick, simple to use, and highly predictive in diverse populations and settings," Dr. Zielinkski says. "There really is no downside."