Introduction: The Revised Atlanta Classification is the standard clinical framework for grading severity in acute pancreatitis, while the CT Severity Index provides an objective radiological measure of pancreatic inflammation and necrosis. This study evaluates the predictive accuracy of the former against the latter as reference standard.

Methods: Patients with acute pancreatitis presenting to a tertiary care teaching hospital were included on accrual over two years. Eighty-nine patients meeting inclusion criteria (age above 18 years, Ranson score of 3 or more, available contrast-enhanced CT) were studied. Severity was graded by both systems, and diagnostic performance of the Revised Atlanta Classification for severe disease was calculated using the CT Severity Index as reference standard.

Results: The 41-50-year age group was most represented (29.2%), with male predominance (65.2%). Abdominal pain (47.2%) was commonest, and alcohol use (25.8%) and gallstones (21.3%) were leading risk factors. By the Revised Atlanta Classification, 49.4% had mild, 34.8% moderately severe, and 15.7% severe disease, concordant with CT Severity Index grading (chi-square 58.72, p<0.001). The Revised Atlanta Classification predicted severe disease with sensitivity 73.3%, specificity 95.9%, positive predictive value 78.6%, negative predictive value 94.7%, and accuracy 92.1% (area under curve 0.85, 95% CI 0.76-0.94, p<0.001). Increasing severity correlated significantly with ICU admission, organ failure, hospital stay, and mortality (p<0.001-0.002).

Conclusion: The Revised Atlanta Classification correlates strongly with the CT Severity Index and reliably predicts severe acute pancreatitis and adverse outcomes, supporting its use as a practical bedside prognostic tool, with the CT Severity Index as a valuable confirmatory measure.