Sensitivity and Specificity of Serial Focused Assessment With Sonography in Trauma (FAST) in Patients With Blunt Abdominal Trauma

TL;DR

The study shows that performing multiple FAST scans over time improves the accuracy of detecting abdominal injuries in trauma patients.

Contribution

The novelty lies in demonstrating how serial FAST exams at 4, 8, and 12 hours improve diagnostic accuracy compared to single-time assessments.

Findings

FAST sensitivity increased from 64.4% at 4 hours to 88.1% at 12 hours.

Specificity improved from 64.3% to 85.7% over the same time intervals.

Positive predictive value remained consistently above 93% across all time points.

Abstract

Introduction

Blunt abdominal trauma (BAT) is a major cause of morbidity and mortality, most frequently resulting from road traffic accidents and falls. Focused assessment with sonography in trauma (FAST) is a rapid, non-invasive, bedside imaging technique used to detect intra-abdominal free fluid. While FAST is widely accessible and radiation-free, its diagnostic accuracy varies with time and clinical context. This study is aimed to evaluate the diagnostic accuracy of serial FAST performed at 4, 8, and 12 hours after injury, using contrast-enhanced computed tomography (CECT) whole abdomen as the reference.

Materials and methods

This was a prospective observational study, conducted at the Department of General Surgery, Ganesh Shankar Vidyarthi Memorial Medical College, Kanpur, Uttar Pradesh, India, between April 2024 and April 2025. A total of 132 adult patients presenting with BAT in emergency were enrolled based on strict inclusion and exclusion criteria. FAST was performed at 4, 8, and 12 hours post-injury. Diagnostic performance was assessed by comparing FAST findings with CECT results in terms of sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV).

Results

Liver injuries were the most common (37.12%), followed by splenic and gastrointestinal injuries (18.18% each). Sensitivity of FAST improved from 64.4% at 4 hours to 76.3% at 8 hours and 88.1% at 12 hours. Specificity also increased from 64.3% to 85.7% across the same intervals. PPV remained consistently high (>93%), whereas NPV increased from 17.6% to 46.2%. The diagnostic improvement over time was statistically significant (p < 0.05 for 8 and 12 hours).

Conclusion

Serial FAST enhances diagnostic accuracy in BAT, particularly when performed at delayed intervals. While a positive FAST is highly predictive of injury, a negative FAST, especially at earlier time points, should be interpreted with caution. Integration of serial FAST into trauma protocols can improve injury detection and clinical outcomes.