About the Bedside Index for Severity in Acute Pancreatitis (BISAP)
BISAP predicts mortality in acute pancreatitis from five criteria, each worth one point: blood urea nitrogen above 25 mg/dL, impaired mental status, SIRS, age over 60, and a pleural effusion. All five are available within the first 24 hours, which is its advantage over Ranson's 48-hour criteria. A score of 2 or below indicates low risk with mortality under about 1%, while 3 or above marks high risk, rising above 20% in the highest group. In the validation cohort of 18,256 cases the AUC for in-hospital mortality was 0.82.
Formula
BISAP = BUN > 25 mg/dL (1)
+ Impaired mental status (1)
+ SIRS ≥ 2 criteria (1)
+ Age > 60 years (1)
+ Pleural effusion (1)- B — BUN
- Blood urea nitrogen above 25 mg/dL. Strictly greater than.
- I — Impaired mental status
- Any disorientation, lethargy, somnolence, coma or stupor.
- S — SIRS
- Two or more of the four systemic inflammatory response criteria.
- A — Age
- Above 60 years. Strictly greater than.
- P — Pleural effusion
- Present on any imaging modality.
- The mnemonic is the score: BISAP spells out its own five criteria.
- All criteria are unweighted — each contributes exactly one point.
- Both numeric thresholds are strict inequalities. BUN of exactly 25 and age of exactly 60 each score zero.
- Enter BUN in mg/dL, or switch the unit toggle if your laboratory reports urea in mmol/L.
Interpreting the result
The practical dividing line is 3. At 2 or below, mortality is low and ward-level care with fluid resuscitation and analgesia is usually appropriate; at 3 or above, mortality climbs steeply and high-dependency or intensive care should be considered. Two caveats matter more than the number. First, BISAP is a first-day snapshot and acute pancreatitis is a disease that declares itself over 48 to 72 hours, so a low score on admission does not license relaxed monitoring — reassess. Second, it predicts mortality, not local complications: a patient with a BISAP of 1 can still develop extensive necrosis, and that is what CTSI is for at around 72 hours.
| Score | Band | What it means | Action |
|---|---|---|---|
| 0–2 | Low risk | Low mortality — under about 1% in the lowest-risk group in the derivation work | Ward-level care with fluid resuscitation and analgesia; reassess at 24 and 48 hours |
| 3–5 | High risk | Substantially higher mortality, exceeding 20% in the highest-risk group | Consider high-dependency or intensive care; aggressive resuscitation with close monitoring; image at ~72 hours if not improving |
Scroll the table sideways for every column.
What the BISAP Score needs (5 inputs)
- Blood urea nitrogen above 25 mg/dL
- 1 point. The threshold is a strict inequality — exactly 25 mg/dL scores zero. BUN is the single strongest laboratory predictor of mortality in acute pancreatitis, and a rising BUN over the first 24 hours is more ominous than a single raised value.
- Impaired mental status
- 1 point. Disorientation, lethargy, somnolence, coma or stupor — anything short of full alertness and orientation. Assessed clinically rather than by a formal score.
- SIRS criteria met
- 1 point for two or more of: temperature below 36 or above 38 °C; heart rate above 90; respiratory rate above 20 or PaCO₂ below 32 mmHg; white cell count below 4 or above 12 ×10⁹/L. Persistent SIRS beyond 48 hours is itself one of the strongest predictors of severe disease.
- Age over 60 years
- 1 point. Again a strict inequality — a patient aged exactly 60 scores zero on this criterion.
- Pleural effusion on imaging
- 1 point. Detected on chest radiograph, CT or ultrasound. Reflects the systemic inflammatory response and third-space fluid loss rather than a pulmonary problem in itself.
Units. Blood urea nitrogen is scored in mg/dL, as reported in the United States. If your laboratory reports urea in mmol/L, switch the unit toggle rather than entering the figure directly — BUN in mg/dL is urea in mmol/L divided by 0.357 (roughly multiplied by 2.8), so a urea of 9 mmol/L is about 25 mg/dL, right at the threshold. Entering urea in mmol/L as though it were BUN in mg/dL will almost always score the criterion as absent when it is present.
What it returns
- BISAP score (0–5)
- One point per criterion met. Simple and unweighted, which is deliberate — every criterion is worth the same, so it can be counted on the fingers of one hand.
- Mortality risk band
- Low or high risk, with the corresponding in-hospital mortality. In the original work mortality ranged from under 1% in the lowest-risk group to over 20% in the highest.
How it is calculated
Wu and colleagues derived BISAP from a very large administrative dataset — 17,992 cases of acute pancreatitis from 212 hospitals — by identifying which routinely recorded variables independently predicted in-hospital mortality, then reducing the model to five binary criteria that could be assessed at the bedside within 24 hours. The deliberate simplification to unweighted single points costs a little discrimination but buys something more valuable in practice: a score that can be calculated correctly by any clinician at any hour without a reference card. It was then validated in a separate cohort of 18,256 cases from 177 hospitals.
Facts & figures
| Letter | Criterion | Threshold | Points |
|---|---|---|---|
| B | Blood urea nitrogen | > 25 mg/dL | 1 |
| I | Impaired mental status | Any alteration | 1 |
| S | SIRS | ≥ 2 of 4 criteria | 1 |
| A | Age | > 60 years | 1 |
| P | Pleural effusion | Present on imaging | 1 |
Scroll the table sideways for every column.
Both numeric thresholds exclude the boundary value: BUN of exactly 25 mg/dL and age of exactly 60 years score zero.
| Parameter | Threshold |
|---|---|
| Temperature | < 36 °C or > 38 °C |
| Heart rate | > 90 bpm |
| Respiratory rate | > 20/min, or PaCO₂ < 32 mmHg |
| White cell count | < 4 or > 12 ×10⁹/L |
Scroll the table sideways for every column.
Evidence
Derivation — US national administrative dataset
2008 · n = 17,99217,992 cases of acute pancreatitis from 212 hospitals in 2000–2001, used to identify and reduce the predictors of in-hospital mortality to five bedside criteria available within 24 hours.
Mortality ranged from under 1% in the lowest-risk group to over 20% in the highest.
Validation — separate national cohort
2008 · n = 18,25618,256 cases of acute pancreatitis from 177 hospitals in 2004–2005, independent of the derivation dataset.
AUC 0.82 (95% CI 0.79–0.84) for predicting in-hospital mortality.
Comparison with Ranson's criteria — meta-analysis
2024 · n = 5,476Systematic review and meta-analysis of 17 studies comprising 5,476 patients with acute pancreatitis, 15 of them in the quantitative analysis, comparing Ranson and BISAP for both severity and mortality.
For severity, pooled sensitivity was 0.95 (95% CI 0.87–0.98) for Ranson against 0.67 (0.27–0.92) for BISAP, and specificity 0.74 (0.52–0.88) against 0.95 (0.85–0.98). For mortality, Ranson 0.89 (0.73–0.96) sensitivity and 0.79 (0.68–0.87) specificity, BISAP 0.77 (0.58–0.89) and 0.90 (0.86–0.93). Overall performance was comparable, with Ranson consistently the more sensitive and BISAP the more specific.
How it compares
BISAP Score vs Ranson's criteria
Use BISAP on day one and Ranson once 48 hours of data exist — pooled across 17 studies Ranson is the more sensitive and BISAP the more specific, and only BISAP is available when the triage decision has to be made.
Ranson's criteria cannot be completed until 48 hours have passed, so they cannot inform the initial decision about level of care. A 2024 meta-analysis of 5,476 patients found Ranson's pooled sensitivity for severity to be 0.95 against BISAP's 0.67, and BISAP's specificity 0.95 against Ranson's 0.74; the pattern held for mortality. So Ranson misses fewer severe cases and BISAP raises fewer false alarms, with comparable overall accuracy. Neither is strictly better — in practice the deciding factor is timing.
BISAP Score vs CTSI
They answer different questions at different times: BISAP predicts mortality on day one, CTSI grades local complications on contrast CT at 72 hours or later.
CTSI combines the Balthazar grade of peripancreatic inflammation with the extent of pancreatic necrosis, so it describes what has happened to the gland. It requires contrast-enhanced CT and is unreliable before about 72 hours because necrosis is not yet visible. BISAP requires no CT and works on day one. A complete assessment of a severe case usually involves both, in that order.
BISAP Score vs APACHE II
APACHE II is at least as accurate but needs around a dozen variables; BISAP achieves comparable discrimination from five bedside criteria, which is why it displaced APACHE II for routine use.
APACHE II was the reference standard for severity in acute pancreatitis and remains widely used in research. It is impractical to calculate repeatedly at the bedside and includes variables not otherwise needed. BISAP's validation AUC of 0.82 for in-hospital mortality is in the same range, from five criteria that can be assessed from an observation chart, one blood test and a chest film.
Pearls & pitfalls
- Both numeric thresholds are strict. A BUN of exactly 25 mg/dL and an age of exactly 60 both score zero, which surprises people expecting 'or above'.
- It predicts mortality, not local complications. A low BISAP does not exclude developing necrosis, and CTSI at around 72 hours is the tool for that question.
- A low score on day one is not a licence to stop watching. Acute pancreatitis declares itself over 48 to 72 hours, and the score should be reassessed.
- SIRS is the criterion most often mis-scored — it needs two of the four parameters, and the white cell and respiratory thresholds are frequently forgotten.
- BUN in mg/dL is not urea in mmol/L. Multiply urea in mmol/L by 2.8 to approximate BUN in mg/dL, or use the unit toggle.
- A rising BUN over the first 24 hours carries more weight clinically than a single value above threshold, even though the score only asks the binary question.
- The pleural effusion criterion needs imaging. If no chest film or CT has been done, the criterion is unassessed rather than absent, and the score will be falsely low.
Critical actions
- Calculate it within the first 24 hours, when it can still change where the patient is nursed.
- At 3 or above, involve critical care early rather than after deterioration.
- Resuscitate with fluid guided by urine output, haematocrit and clinical response, and reassess frequently in the first 48 hours.
- Recalculate or reassess at 24 and 48 hours — a single admission score does not capture a disease that evolves.
- Identify and treat the cause: gallstones need biliary imaging and consideration of urgent ERCP if there is cholangitis, and alcohol needs withdrawal management.
- Image at around 72 hours, or sooner if deteriorating, and use CTSI to assess necrosis rather than expecting BISAP to detect it.
- Do not withhold escalation on the basis of a low score in a patient who looks unwell.
Why this score exists
BISAP was built to be counted, not computed. Its authors had a large enough dataset to fit a weighted model with more variables, and chose not to: every criterion carries one point, and the mnemonic spells the score's own name. That decision trades a little statistical discrimination for something that matters more in a busy admissions unit — a score that a clinician can apply correctly from memory at three in the morning, without a card or an app. The 24-hour constraint was equally deliberate. Ranson's criteria need 48 hours, and the authors' argument was that a prognostic score which arrives after the triage decision has been made is not doing prognostic work.
About the creator
First author, 2008 derivation study
Derived BISAP to predict mortality in acute pancreatitis from five variables obtainable within the first 24 hours.
Senior author
Led the Brigham pancreatitis programme and co-chaired the revised Atlanta classification of acute pancreatitis severity.
Limitations
- Derived from administrative discharge data rather than prospectively collected clinical records, so criteria were captured as coded rather than examined.
- Predicts mortality only — it does not identify necrosis, infected collections or other local complications.
- A single early snapshot of a disease that evolves over 48 to 72 hours; it is not designed for serial use even though clinical reassessment is essential.
- The pleural effusion criterion depends on imaging having been performed, so it is systematically under-recorded where chest imaging is not routine.
- Unweighted criteria discard information — a BUN of 26 mg/dL and one of 90 mg/dL score identically.
- SIRS itself is a non-specific criterion that has fallen out of favour in sepsis definitions, though it remains embedded here.
- Less sensitive than Ranson's criteria for severe disease, so a low score should not override clinical concern.
If you are the patient
BISAP is a way of judging, in the first day of an attack of pancreatitis, how severe it is likely to be. It counts five things: a kidney blood test result, whether you are fully alert, whether your body is showing a strong inflammatory response (temperature, pulse, breathing rate and white cell count), whether you are over 60, and whether there is fluid at the base of a lung on a chest picture. Each counts as one point. A score of 0 to 2 means the attack is likely to be milder and can usually be managed on a normal ward with fluids and pain relief. A score of 3 or more means a higher risk and your team will usually want you somewhere with closer monitoring. Something important to know: pancreatitis can worsen over the first two or three days, so a reassuring score on day one does not mean the team will stop watching closely — they will reassess, and a scan later in the week may be arranged to look at the pancreas itself.
Frequently asked questions
What is the BISAP score?#
BISAP is the Bedside Index for Severity in Acute Pancreatitis. It predicts in-hospital mortality from five criteria, each worth one point: BUN above 25 mg/dL, impaired mental status, SIRS, age over 60, and a pleural effusion. All five are available within 24 hours of admission.
What does a BISAP score of 3 mean?#
A score of 3 or more marks high risk, where mortality rises substantially — exceeding 20% in the highest-risk group in the original work. It indicates that high-dependency or intensive care should be considered, along with aggressive fluid resuscitation and close monitoring.
What are the five BISAP criteria?#
The mnemonic is the name: BUN above 25 mg/dL, Impaired mental status, SIRS (two or more criteria), Age over 60 years, and Pleural effusion on imaging. Each is worth one point and none is weighted more heavily than another.
Is BISAP or Ranson better for acute pancreatitis?#
They trade off against each other. Ranson is more sensitive and BISAP more specific — in one comparison 100% versus 60% sensitivity and 81.2% versus 96.2% specificity for predicting severity. The decisive practical difference is timing: BISAP is complete at 24 hours, Ranson needs 48, so only BISAP can inform the initial decision about level of care.
How accurate is the BISAP score?#
In a validation cohort of 18,256 cases from 177 hospitals, the AUC for in-hospital mortality was 0.82 (95% CI 0.79–0.84). That is comparable to APACHE II, from five criteria instead of around a dozen variables.
Does BISAP detect pancreatic necrosis?#
No. BISAP predicts mortality and says nothing about local complications. Necrosis is assessed on contrast-enhanced CT, usually at 72 hours or later once it becomes visible, and graded with the CT severity index. A patient can have a low BISAP and still develop extensive necrosis.
Is BISAP calculated at exactly 24 hours?#
It is designed to be calculable within the first 24 hours, using the worst values in that window. That is its defining advantage over Ranson's criteria, which cannot be completed until 48 hours have passed. Clinical reassessment should continue regardless of when the score was calculated.
Does a BUN of exactly 25 mg/dL score a point in BISAP?#
No. The criterion is strictly greater than 25 mg/dL, so exactly 25 scores zero. The same applies to age: the criterion is over 60, so a patient aged exactly 60 scores zero on that item.
References
Original / primary reference
Validation and comparison
- 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.
- The Value of BISAP Score for Predicting Mortality and Severity in Acute Pancreatitis: A Systematic Review and Meta-Analysis. PLoS One. 2015;10(6):e0130412.
- Predictive value of the Ranson and BISAP scoring systems for the severity and prognosis of acute pancreatitis: a systematic review and meta-analysis. PLoS One. 2024;19(4):e0302046.
- Evaluation of the BISAP scoring system in prognostication of acute pancreatitis: a prospective observational study. Int J Surg. 2018;54(Pt A):76-81.