SAPS II Score Calculator
The SAPS II calculator estimates in-hospital mortality risk for critically ill patients using 17 physiological variables measured during the first 24 hours in the ICU. Enter age, vital signs, laboratory values, oxygenation status, chronic disease history, and admission type to get the SAPS II score and a predicted mortality probability based on the original Le Gall 1993 logistic regression formula.
Formula
Worked example
A 65-year-old medical patient (12 + 6 = 18 pts) with heart rate 110 bpm (4 pts), SBP 90 mmHg (5 pts), GCS 14 (0 pts), no fever (0 pts), not ventilated (0 pts), urine 800 mL/day (4 pts), BUN 35 mg/dL (6 pts), Na 136 (0 pts), K 4.2 (0 pts), HCO3 21 (0 pts), bilirubin 1.0 (0 pts), WBC 11 (0 pts), no chronic disease (0 pts) produces a SAPS II score of 37. X = -7.7631 + 0.0737 x 37 + 0.9971 x ln(38) = -7.7631 + 2.7269 + 3.6424 = -1.394. Mortality = e^(-1.394) / (1 + e^(-1.394)) = approximately 19.9%.
What is SAPS II?
The Simplified Acute Physiology Score II (SAPS II) is a validated ICU severity-of-illness scoring system developed by Jean-Louis Le Gall and colleagues in 1993. It was derived from a large European and North American multicenter study of over 13,000 ICU admissions. The score is calculated from 17 variables collected during the first 24 hours of an ICU stay and maps directly to a predicted probability of in-hospital death using a logistic regression equation. Unlike organ-failure scores such as SOFA, SAPS II does not require daily reassessment; it is a single snapshot capturing the worst values from the first day of intensive care.
How to use this calculator
Enter all 17 variables from the patient's first 24 hours in the ICU: age, admission type, chronic disease status, heart rate, systolic blood pressure, temperature, Glasgow Coma Scale, oxygenation (PaO2/FiO2 ratio on mechanical ventilation or CPAP), urine output, BUN or serum urea, sodium, potassium, bicarbonate, bilirubin, and white blood cell count. Always use the WORST value recorded in the first 24 hours for each physiological variable (that is, the value that corresponds to the highest number of points). If the patient was not on mechanical ventilation or CPAP at any point during the first 24 hours, set the oxygenation variable to "not ventilated" and no points are scored for that category. For chronic diseases, score only the highest applicable category.
Score interpretation and limitations
A SAPS II score below 25 corresponds to roughly 10% or less predicted in-hospital mortality; a score of 52 corresponds to about 50%; and a score above 77 corresponds to more than 90%. These are population-level estimates based on the original 1993 derivation cohort and may not apply to contemporary ICU populations, specific diagnoses, or single patients. The score was not intended for patients under 18 years old, burns, cardiac surgery, or coronary care unit admissions. Case-mix and treatment intensity have changed substantially since 1993, so the absolute mortality estimates may be systematically high or low in modern units. SAPS II should be used as one component of clinical assessment alongside diagnosis-specific tools (such as SOFA, APACHE II, or CAP severity scores) and clinician judgment, never as a sole decision-making instrument.
Clinical use and evidence base
SAPS II is widely used for benchmarking ICU performance, stratifying patients in research studies, and comparing outcomes across institutions and time periods. It correlates well with APACHE II for most ICU populations and is computationally simpler, which makes it practical for rapid bedside calculation. The original Le Gall 1993 paper (New England Journal of Medicine) reported an area under the receiver operating characteristic curve of 0.88 in the validation cohort, which indicates strong discrimination. Subsequent external validation studies have confirmed acceptable calibration in general ICU populations, although performance can decline in certain subgroups such as neurocritical care or post-cardiac-arrest patients. The scoring table was designed to capture the physiological derangements most strongly associated with mortality in a multivariate model, so each variable and its point bands reflect independent predictive value rather than simply physiological severity.
SAPS II score and predicted in-hospital mortality
| SAPS II score | Predicted mortality | Risk category |
|---|---|---|
| 0-24 | < 10% | Low |
| 25-39 | 10-25% | Low-moderate |
| 40-51 | 25-50% | Moderate-high |
| 52-63 | 50-75% | High |
| 64-76 | 75-90% | Very high |
| 77+ | > 90% | Extremely high |
Approximate mortality thresholds derived from the Le Gall 1993 logistic regression. Individual patient outcomes may differ substantially from population estimates.
Frequently asked questions
What time window does SAPS II use?
SAPS II is calculated from the WORST values of each physiological variable recorded during the first 24 hours of ICU admission. "Worst" means the value that gives the most points for each variable, not necessarily the most extreme in the absolute sense. For example, a heart rate that falls to 35 bpm at some point during the night should be scored as <40 bpm (11 points) even if the rate is 80 bpm at the time of the formal assessment.
How do I score GCS when the patient is sedated?
Use the GCS recorded before sedation or neuromuscular blockade was given, or the best assessment available before sedation. If the patient was sedated from the moment of ICU arrival and no pre-sedation GCS was documented, most guidelines recommend using the GCS at the time sedation was first administered rather than an assumed normal score. Document your assumption when scoring.
What counts as a chronic disease for SAPS II?
SAPS II recognises three chronic conditions: AIDS with defining complications (not just HIV-positive status), metastatic solid cancer (a primary tumor with distant spread confirmed by imaging, surgery, or histology), and hematologic malignancy (lymphoma, leukemia, or multiple myeloma). If more than one applies, score only the highest (AIDS at 17 points, hematologic malignancy at 10 points, or metastatic cancer at 9 points). Stable controlled conditions such as hypertension or diabetes are not scored.
How is the SAPS II mortality probability calculated?
The predicted in-hospital mortality probability is derived from a logistic regression equation published by Le Gall in 1993. The formula is: X = -7.7631 + 0.0737 x SAPS II + 0.9971 x ln(SAPS II + 1). The mortality probability is then e^X / (1 + e^X). This converts the linear score into a probability on a sigmoidal curve between 0 and 1.
How does SAPS II differ from APACHE II?
Both SAPS II and APACHE II are first-24-hour ICU severity scores that predict in-hospital mortality. APACHE II uses 12 acute physiological variables plus age and chronic health points, while SAPS II uses 15 physiological variables plus age, admission type, and chronic disease. SAPS II does not require a diagnosis-specific adjustment (unlike APACHE III), making it simpler to apply. Both scores have similar discrimination in general medical-surgical ICU populations, and the choice between them often depends on local convention and the research or benchmarking context.