How this instrument works
SAPS II (Simplified Acute Physiology Score II) is an ICU severity-of-illness and mortality-prediction score built by Le Gall, Lemeshow, and Saulnier from a European/North American multicenter study, published in JAMA in 1993. It is comparable in scale and stakes to this site's own APACHE II calculator, and this page follows that calculator's structure and tone closely. SAPS II is a clinician-facing instrument for classifying how physiologically deranged an ICU patient is and for predicting hospital mortality risk — used for severity-of-illness classification and for critical-care research and quality-benchmarking work that compares a unit's predicted mortality against its actual observed mortality. It is not a bedside triage tool, not a rule for making an individual patient's treatment decision, and not a patient-facing self-assessment tool.
The score sums 13 individual point components — age, heart rate, systolic blood pressure, temperature, Glasgow Coma Score, oxygenation, urine output, urea, sodium, potassium, bicarbonate, bilirubin, and white blood cell count — with additional points for admission type and chronic disease status, into a single SAPS II total. That total is then run through a closed-form logistic formula, logit = −7.7631 + 0.0737×totalPoints + 0.9971×ln(totalPoints+1), and the logit converts to a predicted hospital mortality percentage via mortality% = e^logit/(1+e^logit)×100. Unlike APACHE II's raw 0-71 point total, SAPS II's output is a direct mortality probability.
Three scoping choices are built into this calculator. Oxygenation (the PaO2/FiO2 ratio) is scored only when the patient is mechanically ventilated or on CPAP — the ventilated field gates whether the ratio field contributes any points at all, and a non-ventilated patient's oxygenation component is always 0 regardless of the ratio entered. Urea is entered in mg/dL, the US-conventional BUN unit, rather than the mmol/L unit the original French-derived paper used; the 28 and 84 mg/dL point-band thresholds are the SI-equivalent converted values, not independently re-derived from scratch. Chronic disease status is a single select rather than three separate yes/no flags, because metastatic cancer, hematologic malignancy, and AIDS are mutually exclusive in the original scoring — a patient with more than one qualifying condition still scores only the single worst-weighted category, never a sum of multiple.
On sourcing: the 1993 primary JAMA paper was not read directly while building this page. The point table above and the exact logistic mortality formula were instead cross-validated against MDCalc's independently published SAPS II calculator, which agrees exactly on every point value and every coefficient used here, and cross-checked against the Wikipedia SAPS II article's description of the score's variables and purpose — see references. Treat the predicted mortality this calculator produces as decision support drawn from a well-corroborated secondary record of the original score, not as a figure independently confirmed against the 1993 paper's own text.
- Enter patient age in years (age) and select the admission type (admission) — scheduled surgical, medical, or unscheduled surgical.
- Enter heart rate (hr), systolic blood pressure (sbp), temperature (temp), and Glasgow Coma Score (gcs).
- Set ventilated (ventilated) to Yes only if the patient is mechanically ventilated or on CPAP, then enter the PaO2/FiO2 ratio (ratio) — it only scores points when ventilated is Yes.
- Enter 24-hour urine output in liters (urine) and urea/BUN in mg/dL (urea) — the US-conventional unit, not the original paper's mmol/L.
- Enter serum sodium (na), potassium (k), bicarbonate (hco3), total bilirubin (bili), and white blood cell count (wbc).
- Select the single worst-applicable chronic disease category (chronic) — none, metastatic cancer, hematologic malignancy, or AIDS — then review the total points, logit, and predicted mortality percentage.
Worked example: septic shock with respiratory failure and metastatic cancer
A 78-year-old is admitted through the unscheduled-surgical pathway (8 admission points), with heart rate 145/min (4 points), systolic blood pressure 65 mmHg (13 points), temperature 39.5°C (3 points), and Glasgow Coma Score 7 (13 points). The patient is mechanically ventilated, so the PaO2/FiO2 ratio of 150 is scored — falling in the 100-199 band for 9 oxygenation points, whereas that same ratio would earn zero points if the patient were not ventilated at all. Running subtotal: 8+4+13+3+13+9 = 50 points.
Age 78 falls in the 75-79 band for 16 age points, just below the 80-and-over band that would score 18. Urine output of 0.3 L/24h (11 points), urea 100 mg/dL (10 points), sodium 122 mmol/L (5 points), potassium 6 mmol/L (3 points), bicarbonate 13 mmol/L (6 points), bilirubin 7 mg/dL (9 points), and white blood cell count 25 ×1000/mm³ (3 points) add 63 more points, and metastatic cancer as the chronic disease category adds 9 further points. Adding all of this to the running subtotal gives a SAPS II total of 122 points. The logit works out to −7.7631 + 0.0737×122 + 0.9971×ln(123) ≈ 6.03, which converts to a predicted hospital mortality of about 99.8%.
Questions
What is the SAPS II score used for?
SAPS II predicts hospital mortality for adult ICU patients from physiology, age, admission type, and chronic disease status recorded during the ICU stay. It is built for clinicians and critical-care researchers — for severity-of-illness classification and for benchmarking predicted versus observed mortality across ICUs in quality and research settings. It is not a bedside triage tool, not a rule for making an individual treatment decision, and not a patient-facing self-assessment tool; a higher score tracks with higher mortality risk in the derivation cohort, but any one patient's course still depends on clinical judgment and factors the score cannot capture.
Why does oxygenation only score points if the patient is ventilated?
The ratio field (PaO2/FiO2) only contributes points when ventilated is set to Yes, meaning the patient is mechanically ventilated or on CPAP. A non-ventilated patient's oxygenation component is always 0, regardless of the ratio value entered, because the original instrument only scored this ratio in patients receiving ventilatory support. When ventilated is Yes, the ratio bands run 11 points below 100, 9 points from 100 up to 200, and 6 points at 200 or above.
Why is urea entered in mg/dL instead of mmol/L?
This calculator asks for urea (BUN) in mg/dL, the US-conventional unit many clinicians already chart in, rather than the mmol/L unit used in the original French-derived SAPS II paper. The 28 and 84 mg/dL point-band thresholds used here are the SI-equivalent converted values, not independently re-derived from first principles — if you know the original paper's mmol/L bands, expect the same clinical breakpoints expressed in mg/dL instead. Enter your urea/BUN value in mg/dL directly; no conversion is needed on your end.
Why is chronic disease a single select instead of three yes/no questions?
SAPS II's three chronic disease categories — metastatic cancer, hematologic malignancy, and AIDS — are mutually exclusive in the original scoring: a patient is scored on whichever single category applies, never summed across more than one. This calculator uses one select (chronic) with four options — none (0 points), metastatic cancer (9 points), hematologic malignancy (10 points), or AIDS (17 points) — so a patient with, say, both a hematologic malignancy and AIDS would still be scored on AIDS alone, the single worst-weighted applicable category, not both added together.
How reliable is the point table and mortality formula behind this calculator?
The 1993 primary JAMA paper by Le Gall, Lemeshow, and Saulnier was not read directly while building this page. Instead, the point table and the exact logistic mortality formula — logit = −7.7631 + 0.0737×totalPoints + 0.9971×ln(totalPoints+1) — were cross-validated against MDCalc's independently published SAPS II calculator, which agrees exactly on every point value and every coefficient used here, and cross-checked against the Wikipedia SAPS II article's description of the score. Treat the predicted mortality as decision support drawn from a well-corroborated secondary record of the original score, not as a figure confirmed against the 1993 paper's own text.
What does the predicted mortality percentage mean?
The mortality percentage converts the SAPS II total points into a probability of hospital death, using logit = −7.7631 + 0.0737×totalPoints + 0.9971×ln(totalPoints+1) and then mortality% = e^logit/(1+e^logit)×100. It reflects the mortality rate observed in the derivation cohort for patients with similar point totals, not a certainty for any individual patient. SAPS II is most often used to compare a predicted mortality rate against an ICU's actual observed mortality rate across a group of patients — a quality-benchmarking use, not an individual prognosis.
How does SAPS II differ from APACHE II?
Both are ICU severity-of-illness scores built around the same idea — summing weighted physiology, age, and chronic health points into a total — and are comparable in scale and stakes, but they use different variables, different point bands, and different endpoints. APACHE II reports a raw 0-71 point total; SAPS II converts its point total through a logistic formula directly into a predicted hospital mortality percentage. Neither substitutes for the other, and neither is a bedside triage or individual treatment-decision tool — both are severity-classification and research/benchmarking instruments.
Can SAPS II be used to decide whether to admit or discharge a patient?
No. SAPS II is a severity-of-illness and mortality-prediction instrument intended for classification, research, and ICU quality-benchmarking — comparing a unit's predicted mortality against its observed mortality across groups of patients — not a bedside triage tool or a rule for an individual admission, discharge, or treatment decision. The predicted mortality percentage describes a cohort-level risk pattern observed at the time of scoring, and it does not account for every factor a clinician weighs when managing one specific patient.
References
- Le Gall JR, Lemeshow S, Saulnier F. A new Simplified Acute Physiology Score (SAPS II). JAMA. 1993;270(24):2957-2963
- MDCalc — SAPS II (Simplified Acute Physiology Score II) calculator
- Wikipedia — SAPS II
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.