SAPS II Calculator (Simplified Acute Physiology Score, predicted ICU mortality)

Understanding the SAPS II calculator — concept and principle

The Simplified Acute Physiology Score II (SAPS II) summarises how ill a patient is during the first 24 hours in intensive care and converts the score into a predicted hospital mortality. ICUs use it to describe case mix, compare outcomes and in research, not to make decisions about individual patients.

17 variables, one score: with the default inputs the result is 55.3% (predicted hospital mortality).

How it is calculated

SAPS II (0–163) = points for 17 variables, using the worst value in the first 24 hours:

12 physiological items: age, heart rate, systolic pressure, temperature, PaO₂/FiO₂ (only if ventilated or on CPAP), urine output, BUN, white cells, potassium, sodium, bicarbonate, bilirubin, Glasgow Coma Scale.
Chronic disease: metastatic cancer 9, haematological cancer 10, AIDS 17.
Admission type: planned surgery 0, medical 6, unplanned surgery 8.

Predicted mortality: logit = −7.7631 + 0.0737 × SAPS II + 0.9971 × ln(SAPS II + 1); risk = e^logit ÷ (1 + e^logit).

The principle

Le Gall and colleagues (1993) derived SAPS II from over 13,000 ICU admissions in Europe and North America. Each variable's points reflect how strongly it predicted death in hospital; a low Glasgow Coma Scale carries the most. The logistic equation turns the total into a probability calibrated to that population.

Worked example

Default inputs: age 68, HR 125, SBP 92, temp 38.4 °C, ventilated with PaO₂ 80 and FiO₂ 50%, urine 0.8 L, BUN 35, WBC 14, K 4.2, Na 137, HCO₃ 18, bilirubin 1.1, GCS 13, no chronic disease, medical admission.

Age 12 + HR 4 + SBP 5 + temp 0 + P/F 160 → 9 + urine 4 + BUN 6 + WBC 0 + K 0 + Na 0 + HCO₃ 3 + bilirubin 0 + GCS 5 + chronic 0 + medical 6 = 54.
Logit = −7.7631 + 0.0737 × 54 + 0.9971 × ln 55 = −7.7631 + 3.9798 + 3.9957 = 0.212.
Predicted hospital mortality = e^0.212 ÷ (1 + e^0.212) = 55.3%; P/F = 160 mmHg.

Each point is the calculator re-run with only “Age (years)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Age (years)	SAPS II score (0–163)
17	42
34	42
51	49
68	54
85	60
102	60
136	60

How to read the result

The predicted mortality describes the average outcome of similar patients in the original cohort. Modern ICUs often have lower mortality than SAPS II predicts, so the score is usually recalibrated locally. Comparing observed with predicted deaths (the standardised mortality ratio) is a common quality measure.

Common mistakes

Using values from after 24 hours or not the worst value.
Scoring PaO₂/FiO₂ in patients not ventilated or on CPAP.
Using the prediction to decide on limiting treatment for one patient.

Keep in mind: This is a severity score for clinicians and researchers, not a prognosis for an individual or a diagnosis.

Frequently asked questions

What is a high SAPS II score?

Higher scores mean higher predicted mortality; a score around 50 corresponds to about 50% in the original equation.

How is SAPS II different from APACHE II?

Both use first-day physiology; they use different variables and equations.

Is there a SAPS 3?

Yes, SAPS 3 (2005) uses data from the first hour of ICU admission.

Sources: Le Gall JR, Lemeshow S, Saulnier F, "A new Simplified Acute Physiology Score (SAPS II) based on a European/North American multicenter study", JAMA 1993;270(24):2957–2963

Checked 9 Nov 2026. Le Gall JR, Lemeshow S, Saulnier F, “A new Simplified Acute Physiology Score (SAPS II) based on a European/North American multicenter study”, JAMA 1993;270(24):2957–2963; point table as listed by HL7 Europe score definitions (“SAPS 2”), mortality equation and variable rules as given by the Société Française d’Anesthésie et de Réanimation (SFAR) score page.

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