APACHE II Score Calculator

APACHE II Score Calculator for Critical Care. Higher totals map to progressively higher predicted hospital mortality. In the original cohort, roughly 0-4 points carried about 4% mortality, 5-9 points about 8%, 10-14 about 15%, 15-19 about 25%, 20-24 about 40%, 25-29 about 55%, 30-34 about 75%, and 35 or more exceeded 80%. The score is not interpreted as a fixed threshold but through the diagnosis-specific mortality equation, so the same total implies different risk for, say, postoperative versus septic patients. The practical action is stratification: identifying high-risk patients for closer monitoring or trial inclusion and standardizing severity when comparing units or cohorts, not dictating individual prognosis.

How this calculator works

APACHE II (Acute Physiology and Chronic Health Evaluation II) sums three components measured within the first 24 hours of ICU admission: an Acute Physiology Score built from 12 routine physiologic variables (temperature, mean arterial pressure, heart rate, respiratory rate, oxygenation via A-a gradient or PaO2, arterial pH, serum sodium, potassium, creatinine with a doubling weight for acute renal failure, hematocrit, white blood cell count, and Glasgow Coma Scale scored as 15 minus GCS), each weighted 0-4 for deviation from normal; an age adjustment (0 points if under 44 rising to 6 points at 75 or older); and chronic health points (2 for elective postoperative admission, 5 for emergency or nonoperative admission) when severe organ insufficiency or immunocompromise is present. The total ranges from 0 to 71. A logistic regression equation then combines the score with a diagnostic weight to estimate hospital mortality risk.

When to use this calculator

Use APACHE II in adult ICU patients, calculated from the worst physiologic values in the first 24 hours after admission, primarily for illness-severity stratification, cohort risk-adjustment, benchmarking, and research comparability rather than bedside triage of an individual. It remains widely embedded in trial eligibility criteria and severity stratification for conditions such as acute pancreatitis. Do not apply it to patients under 16, to burn or coronary bypass populations for which it was not derived, as a serial trend tool (it is a single 24-hour snapshot), or as the sole basis for any withdrawal-of-care or resource-allocation decision for a specific patient.

Inputs used

  • Physiology variables
  • Age
  • Chronic health status

Clinical interpretation

Higher totals map to progressively higher predicted hospital mortality. In the original cohort, roughly 0-4 points carried about 4% mortality, 5-9 points about 8%, 10-14 about 15%, 15-19 about 25%, 20-24 about 40%, 25-29 about 55%, 30-34 about 75%, and 35 or more exceeded 80%. The score is not interpreted as a fixed threshold but through the diagnosis-specific mortality equation, so the same total implies different risk for, say, postoperative versus septic patients. The practical action is stratification: identifying high-risk patients for closer monitoring or trial inclusion and standardizing severity when comparing units or cohorts, not dictating individual prognosis.

Worked example

Consider a 70-year-old emergency medical admission with septic shock: temperature 39.5C (+1), MAP 48 mmHg (+4), heart rate 128 (+3), respiratory rate 32 (+3), PaO2 on room air 58 (+1), arterial pH 7.22 (+3), sodium 148 (+1), potassium 5.4 (+1), creatinine 2.4 mg/dL with acute renal failure (+4 doubled to +8), hematocrit 29 (+2), WBC 22 (+2), GCS 11 giving 15 minus 11 (+4). Acute Physiology Score totals 36; add 5 age points and 5 chronic-health points for cirrhosis, giving APACHE II of 46. A score this high corresponds to predicted hospital mortality well above 80%, flagging an extremely high-risk patient.

Limitations and safety notes

APACHE II was derived from 1979-1982 US ICU data and now systematically overestimates mortality in contemporary practice because of improved supportive care, so raw predicted-mortality figures should be read with caution. It requires arterial blood gas and GCS values that may be unavailable or confounded by sedation, and lead-time bias inflates scores in patients stabilized before ICU transfer. It performs poorly outside its derivation population (pediatrics, burns, cardiac surgery, single-organ admissions) and has been largely superseded for prediction by APACHE III/IV and SAPS II, though it persists for legacy comparability.

Frequently asked questions

When should APACHE II be calculated?

Use the worst physiologic values from the first 24 hours after ICU admission. It is a single admission-window snapshot, not a value to recompute serially through the stay.

Does a high APACHE II score justify withdrawing care?

No. It estimates group-level mortality risk and was never validated to guide individual treatment-limitation decisions. Prognostic and goals-of-care conversations require the full clinical picture, not a score cutoff.

Why does the calculator seem to over-predict deaths?

The model was calibrated on early-1980s ICU cohorts. Advances in sepsis care, ventilation, and organ support mean modern observed mortality is often lower than APACHE II predicts, which is why newer models like APACHE IV and SAPS II are preferred for prediction.

How is the creatinine component scored?

The creatinine points are doubled when acute renal failure is present, so a value that would otherwise score up to 4 can contribute up to 8 points, reflecting the strong prognostic weight of acute kidney injury.

What is the maximum possible score?

The total ranges from 0 to 71, combining up to 60 acute physiology points, 6 age points, and 5 chronic-health points. Scores above the mid-30s are uncommon and carry very high predicted mortality.

References

  • Knaus WA, Draper EA, Wagner DP, Zimmerman JE. APACHE II: a severity of disease classification system. Crit Care Med. 1985. PMID: 3928249.
  • Knaus WA, Wagner DP, Draper EA, et al. The APACHE III prognostic system. Risk prediction of hospital mortality for critically ill hospitalized adults. Chest. 1991. PMID: 1959406.

Editorial review and citation methodology

Reviewed by the Quick Medical Calculator Editorial Team. Last reviewed: March 28, 2026. The review checks calculator inputs, intended population, interpretation, limitations, and source alignment.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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