BISAP Score
Bedside Index for Severity in Acute Pancreatitis — a five-point prognostic score that predicts in-hospital mortality within the first 24 hours of admission using readily available clinical data.
Calculate BISAP Score
Enter the patient’s data from the first 24 hours of admission for acute pancreatitis. The BISAP score uses five bedside parameters — each worth 1 point — to estimate in-hospital mortality risk. The SIRS criterion is assessed using embedded vital sign and WBC inputs below.
SIRS is present when ≥ 2 of 4 criteria are met. Enter the patient’s values to auto-calculate SIRS status, or select the SIRS result directly if you have already assessed it.
The BISAP score is designed for use within the first 24 hours of hospital admission for acute pancreatitis. All five parameters should reflect the patient’s status during this initial period. The score estimates in-hospital mortality risk and helps guide early triage decisions — it is a prognostic tool, not a diagnostic one.
Understanding the BISAP Score
The BISAP score was developed by Wu et al. (2008) as a simplified prognostic tool for acute pancreatitis. It was derived from a database of over 17,000 cases and validated in a separate cohort of more than 18,000 patients — making it one of the largest derivation and validation studies for any pancreatitis severity score.
The key advantage of BISAP over older scoring systems such as Ranson’s criteria is that all five parameters can be assessed within the first 24 hours of admission using routine bedside data — no 48-hour waiting period is needed. The acronym BISAP makes the criteria easy to remember.
The BISAP Mnemonic
Each letter represents one criterion (1 point each):
- B — BUN > 25 mg/dL (>8.9 mmol/L)
- I — Impaired mental status (GCS < 15)
- S — SIRS (≥ 2 of 4 criteria)
- A — Age > 60 years
- P — Pleural effusion on imaging
Score range: 0–5
Worked Example
A 72-year-old presents with acute epigastric pain. BUN is 32 mg/dL, GCS is 15 (alert), temperature 38.4°C, heart rate 102, respiratory rate 18, WBC 14.8 × 10³/µL. Chest X-ray shows a small left pleural effusion.
B — BUN 32 > 25 → +1
I — GCS 15 → 0
S — Temp >38, HR >90, WBC >12 = 3/4 SIRS → +1
A — Age 72 > 60 → +1
P — Pleural effusion present → +1
BISAP = 4 → High risk (~20–50% mortality)
Key principle: The BISAP score identifies patients at higher risk of mortality — it does not predict whether an individual patient will die. A BISAP ≥ 3 suggests the patient may benefit from closer monitoring, earlier ICU involvement, and more aggressive supportive care. A low BISAP score (0–1) is reassuring but does not eliminate the possibility of clinical deterioration.
Interpretation & Mortality Risk
The BISAP score stratifies patients across a wide range of mortality risk. The critical threshold is a score of ≥ 3, which is associated with a substantial increase in mortality, organ failure, and pancreatic necrosis.
| BISAP Score | In-Hospital Mortality | Risk Category | Clinical Implication |
|---|---|---|---|
| 0 | < 1% | Very low | Ward-level care generally appropriate; standard supportive management |
| 1 | ~1–2% | Low | Routine ward care; monitor for deterioration; reassess at 24–48 hours |
| 2 | ~2–5% | Moderate | Consider closer monitoring; early involvement of gastroenterology and/or critical care |
| 3 | ~5–20% | High | High risk of organ failure and necrosis; consider ICU-level care; aggressive resuscitation |
| 4 | ~20–50% | Very high | ICU admission recommended; anticipate organ failure; early multidisciplinary input |
| 5 | > 50% | Critical | Maximum severity; ICU mandatory; full organ support may be required |
The BISAP ≥ 3 threshold is the most clinically useful cut-off. In the original validation study, patients with BISAP ≥ 3 had a mortality rate more than 10 times higher than those with BISAP < 3. This threshold also correlates with increased rates of organ failure (multiorgan dysfunction in ~20% of patients with BISAP ≥ 3 vs ~1% with BISAP < 3) and pancreatic necrosis. Use BISAP ≥ 3 as a trigger for escalation of care.
Clinical Context & Individual Criteria
Each of the five BISAP components reflects a distinct pathophysiological dimension of pancreatitis severity. Understanding why each criterion was selected helps clinicians interpret the score meaningfully rather than applying it mechanically.
Elevated blood urea nitrogen reflects two key processes in severe pancreatitis: third-space fluid losses leading to haemoconcentration, and early renal hypoperfusion from systemic inflammation and capillary leak. BUN rises earlier than creatinine in the setting of prerenal azotaemia, making it a sensitive early marker of intravascular volume depletion.
Wu et al. (2009) separately demonstrated that a rising BUN during the first 24 hours of admission is an independent predictor of mortality in acute pancreatitis — even more so than the absolute BUN value at admission. A BUN that fails to decrease despite fluid resuscitation suggests ongoing third-spacing or inadequate resuscitation and should prompt reassessment of the fluid strategy.
Conversion: BUN (mg/dL) × 0.357 = Urea (mmol/L). BUN > 25 mg/dL is equivalent to Urea > 8.9 mmol/L.
Altered mental status (GCS < 15) in acute pancreatitis is a marker of end-organ dysfunction — either from systemic hypoperfusion (cerebral hypoxia), metabolic derangement (hypocalcaemia, uraemia, hyperglycaemia), or the direct neurotoxic effects of the systemic inflammatory response. It is also a component of the qSOFA score and is independently associated with ICU admission and mortality across many acute conditions.
In clinical practice, any degree of disorientation, confusion, agitation, or reduced consciousness in a patient with acute pancreatitis should be treated as impaired mental status (GCS < 15) for the purposes of BISAP. Subtle confusion may be missed if not specifically assessed — consider a formal GCS or AVPU assessment as part of routine evaluation.
The presence of SIRS (≥ 2 of 4 criteria: temperature, heart rate, respiratory rate/PaCO₂, WBC) captures the intensity of the systemic inflammatory response. In acute pancreatitis, SIRS is driven by the release of pro-inflammatory cytokines (IL-1, IL-6, TNF-α) from the inflamed pancreas and surrounding tissues. Persistent SIRS — present at both admission and 48 hours — is a particularly strong predictor of organ failure and is used in the Revised Atlanta Classification to define moderately severe and severe pancreatitis.
SIRS that resolves within 48 hours (transient SIRS) is associated with a much better prognosis than persistent SIRS. Serial assessment of SIRS status over the first 48–72 hours provides important prognostic information beyond the initial BISAP calculation.
Older age is consistently associated with worse outcomes in acute pancreatitis due to reduced physiological reserve, higher comorbidity burden, and decreased ability to compensate for the haemodynamic stress of systemic inflammation. Patients over 60 are more likely to develop organ failure, less likely to tolerate prolonged nil-by-mouth periods, and have higher rates of complications from interventional procedures.
The age threshold of 60 was identified through regression analysis in the original derivation study as the optimal discriminatory cut-off. Note that Ranson’s criteria use a different age threshold (55 for non-gallstone pancreatitis, 70 for gallstone pancreatitis), which can cause confusion when comparing scoring systems.
Pleural effusion in acute pancreatitis reflects several pathological processes: systemic capillary leak from the inflammatory response, diaphragmatic inflammation from adjacent pancreatic inflammation (particularly left-sided), and transdiaphragmatic lymphatic drainage of pancreatic exudate. Its presence is associated with more severe disease, longer hospital stays, and increased need for ICU admission.
Pleural effusion can be detected on chest X-ray (which is often obtained as part of the initial pancreatitis workup), CT abdomen (which may include the lung bases), or ultrasound. Small effusions may be missed on upright chest X-ray — if clinical suspicion is high, a lateral decubitus view or ultrasound may be more sensitive. The BISAP score counts any pleural effusion, regardless of size or laterality.
BISAP in the first hour: On admission for acute pancreatitis, assess all five BISAP components as part of your initial evaluation: (1) Check BUN on the admission blood panel → (2) Perform a quick GCS assessment → (3) Record vitals and WBC for SIRS → (4) Note the patient’s age → (5) Review the chest X-ray or CT lung bases for pleural effusion. Calculate the BISAP score and document it. A score of ≥ 3 should trigger early escalation and ICU referral.
Special Populations & Considerations
The BISAP score was derived from a large, predominantly adult U.S. population. Its performance may vary in certain patient groups, and clinicians should interpret the score within the broader clinical context.
Patients with alcohol-related pancreatitis may present with altered mental status from acute intoxication rather than organ dysfunction, potentially inflating the BISAP score. Conversely, chronic alcohol use may blunt the SIRS response. When assessing the “I” criterion, consider whether altered mentation is from the pancreatitis itself or from concurrent alcohol intoxication or withdrawal — this distinction affects the prognostic significance of the score.
Pancreatitis caused by severe hypertriglyceridaemia (>1000 mg/dL) may produce a pseudonormal amylase and lipase due to assay interference, delaying diagnosis. The BISAP score itself is not affected by the aetiology, but delayed recognition means the score may be calculated later in the disease course than intended. These patients often have metabolic comorbidities (diabetes, obesity) that independently increase severity.
Gallstone pancreatitis accounts for approximately 40% of all acute pancreatitis cases. The BISAP score applies equally regardless of aetiology, but gallstone pancreatitis has a distinct management pathway — early ERCP within 24 hours may be indicated if concurrent cholangitis or persistent bile duct obstruction is present. The BISAP score should not delay definitive biliary management; rather, it helps determine the level of monitoring required during and after intervention.
Patients with pre-existing chronic kidney disease may have a chronically elevated BUN, which will automatically score 1 point on the BISAP regardless of their pancreatitis severity. This reduces the specificity of the score in this population. Clinicians should consider the trend in BUN from baseline rather than the absolute value. A BUN that is unchanged from the patient’s known baseline may be less prognostically significant than a BUN that has acutely risen.
Paediatric note: The BISAP score has not been validated in children. Paediatric acute pancreatitis is less common and has different aetiological profiles. No widely validated paediatric-specific pancreatitis severity score exists — the DeBanto score has been used in some paediatric studies, but expert clinical assessment remains the primary severity guide in children.
Pancreatitis Severity Scoring Systems Compared
Multiple scoring systems exist for assessing the severity of acute pancreatitis. The BISAP score occupies a useful middle ground — simpler than APACHE II, faster than Ranson’s, and more targeted than generic early warning scores.
| Scoring System | Parameters | Timing | Strengths | Limitations |
|---|---|---|---|---|
| BISAP | 5 criteria | First 24 hours | Simple, bedside, quick, well-validated | Binary thresholds; less granular than APACHE II |
| Ranson’s Criteria | 11 criteria | Requires 48 hours | Widely known; historical significance | Cannot be completed at admission; cumbersome; poor calibration in modern cohorts |
| APACHE II | 12 physiological + age + chronic health | First 24 hours | Most accurate; can be recalculated serially | Complex; 14 variables; not pancreatitis-specific; requires ABG |
| Glasgow (Imrie) Score | 8 criteria | Requires 48 hours | Validated in UK populations | 48-hour delay; less well-known outside UK |
| CTSI (Balthazar) | CT findings + necrosis | 72+ hours (CT at ~72h) | Directly assesses local complications | Requires CT; not useful at admission; radiation exposure |
| HAPS | 3 criteria | Admission | Very simple; identifies non-severe cases | Only identifies low-risk patients; cannot grade severity |
The Revised Atlanta Classification is not a scoring system but rather a classification framework that defines the severity of acute pancreatitis based on clinical outcomes rather than admission parameters. It categorises pancreatitis into three grades: mild (no organ failure, no local or systemic complications), moderately severe (transient organ failure resolving within 48 hours, and/or local complications), and severe (persistent organ failure lasting > 48 hours).
The Atlanta Classification is applied retrospectively — severity is determined by how the patient’s course evolves, not by admission data alone. The BISAP score, by contrast, provides an early prediction of which category a patient is likely to fall into. In practice, the two systems complement each other: BISAP guides initial triage, while the Atlanta Classification defines the final severity grade for documentation and research.
International guidelines (ACG 2013, IAP/APA 2013, AGA 2018) generally recommend using any validated scoring system at admission to stratify severity, rather than mandating a specific score. In practice, the choice depends on your institution’s protocols and available data:
- BISAP — Best for rapid bedside assessment at admission; ideal when you need a quick severity estimate without waiting for additional data or complex calculations.
- APACHE II — Most accurate overall but requires more data; best suited for ICU patients where the full dataset is already being collected.
- Persistent SIRS — Simple and powerful; reassessing SIRS at 48 hours provides strong prognostic information with minimal effort.
- Ranson’s / Glasgow — Historical; require 48 hours for completion; largely superseded by BISAP and APACHE II for early assessment.
Many experts now recommend a multimodal approach: use BISAP at admission, reassess SIRS persistence at 48 hours, obtain CT at 72+ hours if clinically indicated, and classify final severity using the Revised Atlanta Classification.
Common Pitfalls & Limitations
The BISAP score is a well-validated prognostic tool, but like all clinical prediction rules it has important limitations that clinicians must understand to use it safely.
A BISAP score of 0 or 1 is associated with very low mortality (< 2%), but this does not mean the patient cannot deteriorate. Acute pancreatitis is a dynamic disease — patients may develop organ failure, necrosis, or infected collections days to weeks after presentation. A low admission BISAP score reflects the initial severity snapshot only. Patients should be monitored closely for the first 48–72 hours regardless of the admission score, with reassessment of clinical status, inflammatory markers, and organ function.
The BISAP score does not capture delayed complications such as walled-off necrosis, pseudocyst formation, or pseudoaneurysm rupture, which may develop weeks into the illness course.
BUN is influenced by factors beyond pancreatitis severity. Dehydration from any cause (poor oral intake before presentation, vomiting), upper gastrointestinal bleeding (which increases BUN through protein absorption), high-protein diets, corticosteroid use, and pre-existing chronic kidney disease can all elevate BUN independently of pancreatitis-related haemoconcentration. Conversely, patients who have received aggressive pre-hospital or early ED fluid resuscitation may have a lower BUN than their true volume status would suggest.
When interpreting the BUN criterion, consider the clinical trajectory: a BUN that is elevated at admission but rapidly normalises with fluid resuscitation is more reassuring than a BUN that remains elevated or continues to rise despite adequate fluids.
The detection of pleural effusion varies significantly by imaging modality. A standard upright posteroanterior chest X-ray requires approximately 200 mL of fluid to detect a meniscus sign, while lateral decubitus views can detect as little as 50 mL. CT of the abdomen (which often includes the lung bases) and bedside ultrasound are more sensitive for small effusions. This means that whether a patient scores a point for pleural effusion may depend on which imaging they receive — creating a potential source of inconsistency.
The original BISAP validation used chest X-ray and/or CT data. In practice, assess the lung bases on whatever imaging is available. If only an AP portable film is available (common in sicker patients), be aware that small effusions may be missed.
Virtually all patients with acute pancreatitis develop some degree of systemic inflammatory response. Studies have shown that 60–80% of patients with acute pancreatitis meet SIRS criteria at admission, making the SIRS component of BISAP the least discriminating criterion for severity in this specific context. However, its inclusion in BISAP reflects its validated contribution to the overall prognostic model when combined with the other four criteria.
For a more specific assessment of SIRS significance, consider whether SIRS persists at 48 hours — persistent SIRS is a much stronger predictor of organ failure and severe pancreatitis than SIRS at admission alone.
Unlike APACHE II (which can be recalculated daily), the BISAP score was designed for a single assessment within the first 24 hours. It was not validated for serial calculation, and its prognostic value at later time points is uncertain. Clinicians should not repeat the BISAP score on day 2 or day 3 and assume the same mortality estimates apply. For ongoing severity assessment beyond 24 hours, use persistent SIRS status, organ failure definitions (Modified Marshall score), or serial APACHE II scoring.
Quick Reference Summary
| Letter | Criterion | Threshold for +1 Point |
|---|---|---|
| B | BUN | > 25 mg/dL (> 8.9 mmol/L) |
| I | Impaired mental status | GCS < 15 |
| S | SIRS | ≥ 2 of 4 SIRS criteria |
| A | Age | > 60 years |
| P | Pleural effusion | Present on imaging |
The Golden Rule: BISAP is a triage tool, not a treatment guide. A score of ≥ 3 flags a patient who may benefit from ICU-level monitoring, aggressive fluid resuscitation, and early multidisciplinary input — but management decisions should always incorporate the full clinical picture, imaging findings, and the patient’s trajectory over the first 48–72 hours.
Disclaimer & References
For Educational Purposes Only. This calculator and the accompanying clinical information are intended as educational tools for healthcare professionals. They do not replace clinical judgement. Results should be interpreted in the full clinical context. Lab reference ranges vary by institution — verify with your own laboratory. Drug dosages should be confirmed against current prescribing information.
References
- Wu BU, Johannes RS, Sun X, Tabak Y, Conwell DL, Banks PA. The early prediction of mortality in acute pancreatitis: a large population-based study. Gut. 2008;57(12):1698–1703. DOI: 10.1136/gut.2008.152702
- Wu BU, Johannes RS, Sun X, Conwell DL, Banks PA. Early changes in blood urea nitrogen predict mortality in acute pancreatitis. Gastroenterology. 2009;137(1):129–135. DOI: 10.1053/j.gastro.2009.03.056
- Papachristou GI, Muddana V, Yadav D, et al. Comparison of BISAP, Ranson’s, APACHE-II, and CTSI scores in predicting organ failure, complications, and mortality in acute pancreatitis. Am J Gastroenterol. 2010;105(2):435–441. DOI: 10.1038/ajg.2009.622
- Banks PA, Bollen TL, Dervenis C, et al. Classification of acute pancreatitis — 2012: revision of the Atlanta classification and definitions by international consensus. Gut. 2013;62(1):102–111. DOI: 10.1136/gutjnl-2012-302779
- Tenner S, Baillie J, DeWitt J, Vege SS; American College of Gastroenterology. American College of Gastroenterology guideline: management of acute pancreatitis. Am J Gastroenterol. 2013;108(9):1400–1415. DOI: 10.1038/ajg.2013.218
- Working Group IAP/APA Acute Pancreatitis Guidelines. IAP/APA evidence-based guidelines for the management of acute pancreatitis. Pancreatology. 2013;13(4 Suppl 2):e1–e15. DOI: 10.1016/j.pan.2013.07.063
- Singh VK, Wu BU, Bollen TL, et al. Early systemic inflammatory response syndrome is associated with severe and not with mild acute pancreatitis. Clin Gastroenterol Hepatol. 2009;7(11):1247–1251. DOI: 10.1016/j.cgh.2009.08.012
- Ranson JH, Rifkind KM, Roses DF, Fink SD, Eng K, Spencer FC. Prognostic signs and the role of operative management in acute pancreatitis. Surg Gynecol Obstet. 1974;139(1):69–81. PMID: 4834279
- Cho JH, Kim TN, Chung HH, Kim KH. Comparison of scoring systems in predicting the severity of acute pancreatitis. World J Gastroenterol. 2015;21(8):2387–2394. DOI: 10.3748/wjg.v21.i8.2387