Ranson's Criteria for Acute Pancreatitis
Ranson's criteria is a validated 11-parameter scoring system that predicts severity of acute pancreatitis with 70-80% accuracy, requiring 48 hours to complete, with ≥3 positive criteria indicating severe disease—however, modern guidelines recommend using it in combination with faster scoring systems like BISAP or APACHE II rather than relying on it alone. 1
What Ranson's Criteria Measures
Ranson's criteria evaluates 11 clinical and laboratory parameters measured at two time points 1:
At admission (0 hours):
- Age >55 years
- White blood cell count >16,000/mm³
- Blood glucose >200 mg/dL
- Serum lactate dehydrogenase (LDH) >350 IU/L
- Aspartate aminotransferase (AST) >250 IU/L
At 48 hours:
- Hematocrit decrease >10%
- Blood urea nitrogen (BUN) increase >5 mg/dL
- Serum calcium <8 mg/dL
- Arterial PO₂ <60 mmHg
- Base deficit >4 mEq/L
- Fluid sequestration >6 liters
Interpretation and Performance
A Ranson score ≥3 indicates severe acute pancreatitis with the following performance characteristics 1, 2:
- Sensitivity: 75-87%
- Specificity: 68-77.5%
- Positive predictive value: 28.6-49%
- Overall prognostic accuracy: 70-80%
Mortality correlates directly with score 4, 2:
- Ranson score ≥3: 22.5% mortality rate
- Ranson score <3: 2.4% mortality rate
The 48-hour Ranson variables (particularly BUN, calcium, base deficit, and fluid sequestration) predict adverse outcomes more accurately than the admission variables 2.
Critical Limitations
The major disadvantage of Ranson's criteria is the mandatory 48-hour delay before completion, which prevents early risk stratification when it matters most for mortality reduction 5, 3. Clinical assessment alone misclassifies approximately 50% of patients, and failure to stratify severity early can result in potentially avoidable deaths 5.
The positive predictive value of only 28.6-49% means that many patients classified as severe will have uncomplicated recovery, while the scoring system does not accurately predict the degree of pancreatic necrosis 5.
Recommended Clinical Approach
Do not wait 48 hours to initiate aggressive management—use complementary scoring systems for immediate risk assessment 6:
Within 24 hours of admission:
- Calculate BISAP score immediately (can identify severe disease within 24 hours with AUC 0.80) 7
- Measure baseline C-reactive protein 7
- Calculate APACHE II score (≥8 indicates severe disease; can be used for daily monitoring) 5, 7
- Assess for clinical organ failure (pulmonary, circulatory, or renal insufficiency) 5
At 48 hours:
- Complete Ranson score calculation 1
- Measure CRP (≥150 mg/L on day 3 indicates severe disease with 80% accuracy) 5, 7
Days 3-10:
- Perform contrast-enhanced CT scan in all patients with predicted severe disease to assess pancreatic necrosis and calculate CT Severity Index 1, 7
Comparison with Alternative Systems
The British Society of Gastroenterology recommends using Glasgow score and CRP rather than Ranson's criteria, as the Glasgow criteria have been specifically validated in UK populations with equivalent 70-80% accuracy 5. The APACHE II score provides equivalent accuracy to Ranson's with the advantage of allowing daily monitoring for disease progression 5, 8.
BISAP score has largely superseded Ranson's criteria in modern practice because it can be calculated within 24 hours with comparable accuracy (AUC 0.80 for severe pancreatitis, 0.93 for organ failure) 7.
Common Pitfalls to Avoid
- Never delay ICU transfer or aggressive fluid resuscitation while waiting for the 48-hour Ranson score to complete 6
- Do not use Ranson's criteria as the sole prognostic tool—combine with BISAP, CRP, and APACHE II for comprehensive risk assessment 6
- Do not administer prophylactic antibiotics based solely on high Ranson score—antibiotics should be reserved for documented infected necrosis only 6
- Do not perform CT imaging before day 3, as early imaging underestimates the extent of necrosis 6