Sensitivity and Specificity of the FAST Exam

Previous studies on the use of the FAST exam in nonpregnant adult blunt trauma patients have found the FAST exam’s detection rate to vary from 79 percent to 98 percent.^15-18 Several studies have attempted to establish the utility of FAST exams as similar in pregnant and nonpregnant women, but the relatively small sample sizes for calculating sensitivity render the findings difficult to rely upon.

When Goodwin and colleagues looked at the use of abdominal ultrasonography to examine pregnant blunt trauma patients, they found a sensitivity of 83 percent (95 percent confidence interval [CI], 36–100 percent) and a specificity of 98 percent (95 percent CI, 93–100 percent). Their sensitivity value determination was  based on an evaluation of only six sonographers—although the total sample size  was 127 patients.¹⁹

Brown and colleagues found the sensitivity of screening sonography for use in pregnant patients with blunt abdominal trauma to be 80 percent (95 percent CI, 28–100 percent), but only used five patients to determine this value.²⁰ Although their reported specificity was 100 percent (95 percent CI, 96–100 percent) for 96 patients without abdominal injury, Brown et al concluded that they “cannot make strong conclusions about sensitivity on the basis of this small study.”²⁰

In a 10-year retrospective study of ultrasound evaluations in pregnant abdominal trauma patients, Meisinger and colleagues determined the sensitivity and specificity of their institution’s extended FAST exam to be 85.7 percent and 99.7 percent, respectively. However, their sensitivity value was calculated based on the findings of only seven patients, and the researchers attributed their higher sensitivity value to the greater training of their sonographers.²¹

A study by Richards and colleagues had the largest number of positive cases (n=23) from which a calculation for sensitivity of the FAST exam could be estimated. They found the sensitivity to be 61 percent, the lowest of all the studies. This low sensitivity compelled them to conclude that the FAST exam “does not rule out intra-abdominal pathology.”²² Their specificity was 94.4 percent for 288 out of 305 patients.²² Taken together, the sensitivity values in the existing literature, which were calculated based on small sample sizes and have large margins of error, are uncertain indicators of the FAST examination’s reliability in detecting signs of blunt trauma within pregnant patients. However, the high specificity in these studies suggests that the presence of positive findings may be enough information to act upon.