SAPS II Calculator — Simplified Acute Physiology Score
Select the worst values recorded in the first 24 hours of ICU admission to compute the SAPS II score and its associated predicted hospital mortality. For educational and research use — not a substitute for clinical judgment.
Age
Heart rate (worst 24 h)
Systolic BP (worst 24 h)
Temperature (highest)
Glasgow Coma Scale
PaO₂/FiO₂ (if ventilated)
Urine output
Blood urea nitrogen
White blood cells
Serum potassium
Serum sodium
Serum bicarbonate
Serum bilirubin
Type of admission
Chronic disease
Simplified Acute Physiology Score II (range 0–163)
- 1
SAPS II score (sum of variable points)
18 - 2
ln(score + 1)
ln(18 + 1) = 2.9444 - 3
Logit
−7.7631 + 0.0737 × 18 + 0.9971 × 2.9444 = -3.5006 - 4
e^logit
e^(-3.5006) = 0.0302 - 5
Predicted ICU mortality
0.0302 ÷ (1 + 0.0302) × 100 = 2.9Logistic transformation maps the logit to a predicted mortality probability.
How does this calculator work?
SAPS II sums points for 15 clinical variables (physiological worst values in first 24 h) to produce a score of 0–163. Predicted hospital mortality is calculated as e^logit / (1 + e^logit), where logit = −7.7631 + 0.0737 × score + 0.9971 × ln(score + 1). It is a research/audit tool, not an individual prognosis.
Formula
How this is calculated
SAPS II (Simplified Acute Physiology Score II) was developed by Le Gall et al. and published in JAMA in 1993. It scores 15 clinical variables — demographic, physiological, laboratory, and disease-related — using the worst values from the first 24 hours of ICU admission. Points for each variable were determined by logistic regression against hospital mortality in a large multinational ICU dataset (n = 13 152 patients). The total score can range from 0 to 163, with higher scores indicating greater physiological derangement.
The predicted hospital mortality is derived from the total score using a validated logistic function: logit = −7.7631 + 0.0737 × SAPS II + 0.9971 × ln(SAPS II + 1), then mortality = e^logit / (1 + e^logit). A score of 18 corresponds to roughly 3 % predicted mortality; a score of 55 corresponds to roughly 40 %. The original paper reported an area under the ROC curve of 0.88, indicating good discrimination.
IMPORTANT limitations: SAPS II was calibrated on a 1991–1992 European and North American ICU population. Predicted mortality may be systematically miscalibrated in populations that differ from the original (e.g., cardiac surgery, paediatric, or modern ICUs with updated treatment protocols). It is intended as a research and audit tool for comparing severity across patient groups — individual mortality predictions carry wide confidence intervals and must not replace clinical assessment.
Frequently asked questions
Use the worst (most abnormal) value for each physiological variable during the first 24 hours of ICU admission, as that is how the score was originally defined and validated. The worst heart rate and systolic BP are the extreme values (highest or lowest, whichever scores more points); temperature uses the highest value.
Scores below 20 are associated with predicted mortality under ~5 %. Scores of 40–60 correspond to predicted mortalities of roughly 25–55 %. Scores above 70 are associated with predicted mortalities exceeding 70 %. In clinical practice, the distribution of SAPS II scores at admission varies greatly by ICU type and case mix.
No — the predicted mortality from SAPS II is a group-level statistical estimate derived from logistic regression, not an individual prognosis. Confidence intervals for individual predictions are very wide. The score is best used for case-mix adjustment in research or quality benchmarking, not for individual treatment decisions.
Also known as
TG we-Calculate Editorial Team. (2026). SAPS II Calculator — Simplified Acute Physiology Score [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/saps-ii-calculator
TG we-Calculate Editorial Team. "SAPS II Calculator — Simplified Acute Physiology Score." TG we-Calculate. 2026. https://we-calculate.com/calculator/saps-ii-calculator.
TG we-Calculate Editorial Team, "SAPS II Calculator — Simplified Acute Physiology Score," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/saps-ii-calculator
@misc{wecalculate_saps_ii_calculator, title = {SAPS II Calculator — Simplified Acute Physiology Score}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/saps-ii-calculator}}, year = {2026}, note = {TG we-Calculate} }
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