APACHE II Score Calculator - ICU Severity & Mortality Prediction
Free APACHE II calculator with all 12 physiologic variables, age points, and chronic health evaluation. Instant ICU mortality estimation with severity classification.
APACHE II Assessment
Enter the worst value from the first 24 hours of ICU admission for each variable.
Vital Signs
Worst value in first 24h. Use rectal temperature.
MAP = (SBP + 2×DBP) / 3. Worst value in first 24h.
Worst value in first 24h.
Worst value in first 24h (ventilated or non-ventilated).
Blood Gas / Oxygenation
If FiO2 ≥50%, use A-aDO2. If FiO2 <50%, use PaO2. Worst value in first 24h.
Worst value in first 24h. If no ABG, use serum HCO3 (venous).
Chemistry
Worst value in first 24h.
Worst value in first 24h.
Worst value in first 24h. Double points if acute renal failure (see next input).
If yes, creatinine points are DOUBLED. ARF = acute rise in creatinine not due to chronic kidney disease.
Hematology
Worst value in first 24h.
Worst value in first 24h.
Neurologic
Points = 15 − GCS. If sedated, estimate pre-sedation GCS.
Demographics & Chronic Health
Organ insufficiency or immunocompromise present BEFORE this admission. See reference below for qualifying conditions.
Critical Scoring Reminders
Chronic Health Qualifying Conditions
Must have been present before this hospital admission.
APACHE II Score
Enter values to calculate
About This Calculator
What is the APACHE II Score?
The APACHE II (Acute Physiology and Chronic Health Evaluation II) score is the most widely used ICU severity scoring system in the world, published by Knaus et al. in 1985. It combines 12 acute physiologic variables (worst values in first 24 hours), age points (0–6), and chronic health points (0–5) to produce a score from 0–71 that correlates with ICU mortality risk.
How does APACHE II work?
APACHE II uses the most deranged (worst) values for each of 12 physiologic variables during the first 24 hours of ICU admission. Each variable scores 0–4 points for both high and low abnormal ranges. The Glasgow Coma Scale contributes 0–12 points (calculated as 15 minus actual GCS). Age and chronic health status add additional points. Higher total scores indicate greater severity and higher predicted mortality.
Clinical Applications
- ICU quality benchmarking — comparing observed vs expected mortality rates
- Research enrollment and stratification in clinical trials
- Resource allocation during ICU capacity crises
- Prognostic communication with families
- Administrative reporting and compliance documentation
Important Limitations
APACHE II was derived from 1979–1982 data and systematically overestimates mortality by modern standards. APACHE IV (2006) is now recommended for benchmarking, but APACHE II remains dominant in research due to decades of published comparisons and its open-access nature.
Formula
APACHE II = Acute Physiology Score (0–60) + Age Points (0–6) + Chronic Health Points (0–5); Range 0–71Sum of 12 physiologic variable scores (worst values in first 24 hours, each 0–4 for both high and low derangement), GCS points (15 − GCS), age points, and chronic health points. Unmeasured variables are scored as 0 (assumed normal).
Clinical Considerations
- •APACHE II uses the WORST value in the first 24 hours — not admission values, not averages.
- •Derived from 1979–1982 data — systematically overestimates mortality by modern standards.
- •Score alone is insufficient for mortality prediction — diagnosis-specific coefficients required for precise estimates.
- •Creatinine points are DOUBLED for acute renal failure — always check the ARF toggle.
- •CABG patients should be excluded — anesthetic management falsely elevates scores despite ~1.5% mortality.
- •Unmeasured variables are scored as 0 (assumed normal) — may underestimate severity in under-resourced settings.
Limitations
- •Derived from 1979–1982 data (5,815 patients) — treatment standards have fundamentally changed.
- •51% of manually calculated scores change when retrospectively reassessed (average change: 6.4 points).
- •Static single-timepoint — captures only first 24 hours; does not account for treatment response.
- •GCS confounded by sedation — "assumed GCS" is inherently subjective.
- •Not validated for burns, trauma, liver failure, HIV, or pediatric populations.
- •APACHE IV (2006) is now recommended for benchmarking due to better calibration.
- •Lead-time bias — not accurate for transferred patients already treated at referring hospital.
Interpretation Guide
| Range | Classification | Recommendation |
|---|---|---|
| <-4 | Low Risk | Low severity illness. Monitor with standard ICU care. Good prognosis expected. |
| 5-9 | Low-Moderate Risk | Low-moderate severity. Standard ICU monitoring and management. |
| 10-14 | Moderate Risk | Moderate severity. Active ICU management warranted. Consider Day-3 re-assessment for trajectory. |
| 15-19 | Moderate-High Risk | Moderate-high severity. Aggressive ICU management. Score ≥17 on Day 3 is the optimal mortality cutoff (sensitivity 92.8%). |
| 20-24 | High Risk | High severity with significant mortality risk. Consider goals-of-care discussion. Serial APACHE II trending recommended. |
| 25-29 | Very High Risk | Very high severity. Mortality exceeds 50% for nonoperative patients. Goals-of-care discussion strongly warranted. |
| 30-34 | Critical | Critical illness with very high mortality. Goals-of-care discussion essential. |
| 35-71 | Near-Certain Mortality | Score ≥35 almost invariably portends death. Palliative care consultation and goals-of-care discussion are priorities. |
Frequently Asked Questions
What is the APACHE II score?
APACHE II (Acute Physiology and Chronic Health Evaluation II) is an ICU severity scoring system that combines 12 acute physiologic variables (worst values in first 24 hours), age points, and chronic health status to produce a score from 0–71. Higher scores indicate greater illness severity and higher predicted ICU mortality. It was published by Knaus et al. in 1985 and remains the most widely used ICU severity score worldwide.
How do you calculate the APACHE II score?
APACHE II = Acute Physiology Score + Age Points + Chronic Health Points. The Acute Physiology Score uses the worst value in the first 24 hours for each of 12 variables (temperature, MAP, heart rate, respiratory rate, oxygenation, arterial pH, sodium, potassium, creatinine, hematocrit, WBC, and GCS). Each scores 0–4 for derangement. Age adds 0–6 points. Chronic health adds 0, 2, or 5 points.
What APACHE II score predicts death?
An APACHE II score of ≥25 carries >50% nonoperative mortality risk. Scores ≥35 almost invariably portend death (85–90%+ mortality). A score ≥17 on Day 3 of ICU admission is the optimal cutoff for identifying high-mortality patients (sensitivity 92.8%, specificity 82.2%). Day-3 APACHE II is a stronger predictor than admission APACHE II.
What is a normal APACHE II score?
An APACHE II score of 0 indicates no physiologic derangement, age <45, and no chronic health conditions. Scores of 0–4 represent low risk with approximately 1–4% mortality. A healthy young adult admitted to the ICU for routine postoperative monitoring would typically score 0–4.
What is the difference between APACHE II and APACHE IV?
APACHE II (1985) uses 12 variables from 5,815 patients (1979–82) and is open-access. APACHE IV (2006) uses 17 variables from 110,558 patients (2002–03) with contemporary calibration and is proprietary (Cerner). APACHE IV is recommended for benchmarking due to better calibration, but APACHE II remains dominant in research due to decades of published comparisons.
How does APACHE II compare to SOFA score?
APACHE II and SOFA answer different questions. APACHE II (0–71) provides a one-time admission severity estimate using first-24h data for mortality prediction. SOFA (0–24) tracks 6 organ systems serially for daily dysfunction monitoring and defines sepsis (Sepsis-3). APACHE II is for prognosis; SOFA is for dynamic organ dysfunction tracking. Both are useful; neither replaces the other.
Should you use worst values or admission values for APACHE II?
APACHE II uses the WORST (most deranged) value in the first 24 hours of ICU admission for each variable — not admission values, not averages. You must review the entire first ICU day to find the most abnormal value for each of the 12 physiologic variables. This is a critical distinction that affects scoring accuracy.
How is the creatinine score doubled for acute renal failure?
If a patient has acute renal failure (acute rise in creatinine, not chronic kidney disease), the creatinine points are doubled. For example, creatinine ≥3.5 mg/dL normally scores 4 points, but with ARF it scores 8 points. This can significantly increase the total APACHE II score.
What are chronic health points in APACHE II?
Chronic health points are 0, 2, or 5 based on pre-existing conditions: biopsy-proven cirrhosis with portal hypertension, NYHA Class IV heart failure, severe chronic pulmonary disease, chronic dialysis, or immunocompromise. Elective postoperative patients with these conditions get 2 points; nonoperative or emergency postoperative patients get 5 points.
Is APACHE II still used?
Yes, APACHE II remains the most widely used ICU severity score globally, primarily in research for cross-study comparisons across decades. However, its performance has deteriorated because it was derived from 1979–1982 data and systematically overestimates mortality. APACHE IV is now recommended for quality benchmarking. Several national registries have discontinued APACHE II in favor of newer systems.
What are the limitations of APACHE II?
Key limitations: (1) Derived from 1979–1982 data — systematically overestimates mortality. (2) 51% of manually calculated scores change when reassessed. (3) Static single-timepoint — captures only first 24 hours. (4) GCS confounded by sedation. (5) Score alone is insufficient — requires diagnostic category for mortality prediction. (6) Not validated for all populations (burns, trauma, liver failure, pediatrics). (7) CABG patients are excluded due to falsely elevated scores.
How is oxygenation scored in APACHE II?
Oxygenation scoring depends on the FiO2 level: If FiO2 ≥50%, use the A-aDO2 (alveolar-arterial oxygen gradient). If FiO2 <50%, use PaO2 directly. This conditional logic is the most commonly misscored variable in APACHE II. A-aDO2 ≥500 or PaO2 <55 scores 4 points.
References
1. Knaus WA, Draper EA, Wagner DP, Zimmerman JE. APACHE II: A severity of disease classification system. Critical Care Medicine. 1985
View Source →2. Ferreira FL, Bota DP, Bross A, et al.. Serial evaluation of the SOFA score to predict outcome in critically ill patients. JAMA. 2001
3. Zimmerman JE, Kramer AA, McNair DS, Malila FM. APACHE IV: Hospital mortality assessment for today's critically ill patients. Critical Care Medicine. 2006
4. Polderman KH, et al.. Accuracy and reliability of APACHE II scoring in two intensive care units. Anaesthesia. 2001
View Source →5. Vincent JL, Moreno R. Scoring systems in the critically ill. Critical Care. 2010
View Source →Last updated: 2026-02-25
Related Calculators
SOFA Score
Free SOFA score calculator for ICU organ dysfunction assessment. 6 organ systems with mortality prediction, Sepsis-3 criteria evaluation, and delta-SOFA guidance.
qSOFA
Free qSOFA calculator for bedside sepsis screening. 3 criteria — respiratory rate, blood pressure, mental status — with instant interpretation, SIRS comparison, and Hour-1 Bundle guidance.
CURB-65
Calculates the CURB-65 score to assess the severity of community-acquired pneumonia (CAP) and guide treatment decisions regarding hospitalization vs outpatient management.
NIHSS
Free online NIHSS calculator with guided scoring for all 15 items. Instant stroke severity classification, tPA eligibility assessment, and thrombectomy threshold guidance.
Auto-Calculate APACHE II in Your Clinical Notes
PatientNotes AI automatically captures patient data during your visit and calculates relevant clinical values directly in your documentation. No manual entry needed—just review and approve.
7-day free trial • No credit card required • HIPAA compliant