What is the purpose and calculation of the BISAP (Bedside Index for Severity in Acute Pancreatitis) score in assessing acute pancreatitis severity in adult patients?

BISAP Score: Purpose and Calculation

The BISAP (Bedside Index for Severity in Acute Pancreatitis) score is a simplified 5-point prognostic tool that can be calculated within the first 24 hours of presentation to identify patients at increased risk of mortality and severe disease, with a score ≥3 indicating significantly elevated risk and a score ≥2 serving as a clinically meaningful cutoff for severe acute pancreatitis and organ failure. 1

Calculation Method

Score 1 point for each of the following criteria present within 24 hours:

• Blood urea nitrogen (BUN) > 25 mg/dL (>8.9 mmol/L) 1
• Impaired mental status (disorientation, lethargy, coma) 1
• Systemic inflammatory response syndrome (SIRS) present 1
• Age > 60 years 1
• Pleural effusion detected on imaging 1

Total possible score: 0-5 points 1

Clinical Purpose and Performance

Primary Outcome: Mortality Prediction

• BISAP ≥3 predicts mortality with 56% sensitivity and 91% specificity, with positive likelihood ratio of 5.65 2
• The score demonstrates similar accuracy to APACHE-II for predicting death (AUC 0.82-0.86 vs 0.87) but is far simpler to calculate 3, 4, 5
• Critical advantage: BISAP identifies patients at increased risk of mortality BEFORE the onset of organ failure, unlike traditional scoring systems 1

Secondary Outcomes: Severity and Organ Failure

• BISAP ≥2 is the statistically significant cutoff for severe acute pancreatitis, organ failure, and mortality 1, 4
• For organ failure prediction, BISAP achieves AUC of 0.93, performing as well as APACHE-II (0.95) and superior to Ranson criteria (0.84) 4
• BISAP ≥3 increases risk of organ failure 7.4-fold, persistent organ failure 12.7-fold, and pancreatic necrosis 3.8-fold 5

Key Advantages Over Traditional Scoring Systems

Timing Advantage

• BISAP can be calculated within the first 24 hours of admission, while Ranson and APACHE-II require 48 hours for full assessment 1
• This enables immediate risk stratification on admission rather than waiting 2 days 1

Simplicity Advantage

• All five BISAP components are clinically relevant and routinely available 3
• No complex physiological calculations required, unlike APACHE-II's 12 parameters 6
• Can be calculated at bedside without specialized software 1

Comparative Performance

• BISAP outperforms Ranson criteria, CT severity index, CRP, hematocrit, and BMI for predicting severity and organ failure 1, 4
• BISAP shows higher specificity (91%) compared to Ranson (68-77.5%) and APACHE-II, though with lower sensitivity 2
• The World Journal of Emergency Surgery guidelines note that BISAP was derived from 17,992 patients and validated on 18,256 patients in the USA 1

Clinical Application Algorithm

Score 0-1: Low Risk

• Mortality risk minimal 5
• Standard ward-level care typically appropriate 5
• Continue monitoring for clinical deterioration 5

Score 2: Intermediate Risk

• This is the cutoff for severe acute pancreatitis and organ failure 1, 4
• Consider ICU-level monitoring or step-down unit 7
• Aggressive fluid resuscitation and close surveillance required 7

Score ≥3: High Risk

• Significantly elevated mortality risk 1, 2, 5
• ICU admission strongly recommended 7
• Monitor for development of organ failure, which defines severe disease 7
• Serial procalcitonin measurements to detect infected necrosis 7
• Contrast-enhanced CT between days 3-10 to assess for necrosis 7

Important Clinical Caveats

Limitations to Recognize

• BISAP has suboptimal sensitivity (51-56%) for both mortality and severe disease, meaning it will miss some high-risk patients 2
• The positive predictive value varies by population and disease prevalence 1
• Do NOT use BISAP score alone—complement with clinical judgment, CRP at 48-72 hours, and CT severity index 7

Common Pitfalls to Avoid

• Do NOT delay aggressive management waiting for BISAP calculation—initiate fluid resuscitation immediately based on clinical presentation 7
• Do NOT administer prophylactic antibiotics based on high BISAP score alone—antibiotics are only indicated for documented infected necrosis, not for risk stratification 1, 7
• Do NOT obtain CT scan in first 72 hours based solely on BISAP score—imaging before day 3 underestimates extent of necrosis 7
• Remember that even BISAP score of 1-2 does not guarantee benign course—one patient with BISAP of 1 died in the validation cohort 3

Enhanced Scoring Considerations

• Adding obesity (BMI >25) to BISAP (creating "BISAP-O") may improve sensitivity to 75% and accuracy to 92.3% for severity prediction 8
• Consider calculating both BISAP and APACHE-II scores, as they provide complementary information 4