APACHE II Score Calculator

Acute Physiology and Chronic Health Evaluation II for ICU mortality prediction.

Note

Important Health Disclaimer

This calculator provides general health information based on standard medical formulas and WHO guidelines. Results are for informational and educational purposes only and should not be considered as professional medical advice or a personal care recommendation.

For health concerns, medical conditions, fitness plans, or dietary decisions, please consult with qualified healthcare professionals, licensed physicians, registered dietitians, or certified fitness trainers who can evaluate your individual health status and medical history.

Individual health needs vary significantly. These calculations are general estimates and may not be appropriate for everyone, especially those with existing medical conditions, pregnant women, children, or elderly individuals.

Not a substitute for qualified professional guidance

Physiologic Variables

temperature

mean Arterial Pressure

heart Rate

respiratory Rate

oxygenation

arterial P H

sodium

potassium

creatinine

hematocrit

wbc

gcs

Age Points

Chronic Health Points

APACHE II Score

Estimated Mortality: ~4%

Physiology Score

Age + Chronic

Clinical Interpretation

Low risk. Standard ICU monitoring appropriate.

Score Interpretation

0-9: Low mortality (<10%)
10-19: Moderate mortality (15-25%)
20-29: High mortality (40-55%)
30+: Very high mortality (>75%)

What Is the APACHE II Score?

The APACHE II (Acute Physiology And Chronic Health Evaluation II) score is the most widely used severity-of-illness scoring system in intensive care units worldwide. Developed by Knaus et al. in 1985, it combines 12 acute physiological variables, age, and chronic health status to predict hospital mortality risk for critically ill patients. The score ranges from 0 to 71, with higher scores indicating greater severity of illness and higher predicted mortality.

APACHE II is calculated within the first 24 hours of ICU admission using the worst (most deranged) values for each physiological variable. The 12 variables include: temperature, mean arterial pressure, heart rate, respiratory rate, oxygenation (A-aDO2 or PaO2), arterial pH, serum sodium, serum potassium, serum creatinine, hematocrit, white blood cell count, and Glasgow Coma Scale. Each variable is scored from 0 (normal) to 4 (most abnormal), producing a physiological score of 0-60.

Age points (0-6) and chronic health points (0-5 for severe organ insufficiency or immunocompromise) are added to the physiological score. The total APACHE II score correlates strongly with mortality: scores of 0-4 carry approximately 4% mortality, while scores above 35 have approximately 85% mortality. APACHE II is used for ICU quality benchmarking, clinical research, and guiding treatment intensity decisions.

APACHE II Scoring Structure

The total APACHE II score consists of three components:

APACHE II Score Formula

Total Score = Acute Physiology Score + Age Points + Chronic Health Points

Where:

Acute Physiology Score= Sum of points for 12 physiological variables (0-60). Each scored 0-4 based on worst value in first 24 hours. GCS component = 15 minus actual GCS.
Age Points= ≤44: 0 pts, 45-54: 2 pts, 55-64: 3 pts, 65-74: 5 pts, ≥75: 6 pts
Chronic Health= 0 pts for none. 2 pts for nonoperative/emergency postop with organ failure. 5 pts for elective postop with organ failure.

APACHE II Score and Predicted Mortality

Score Range	Predicted Mortality	Clinical Recommendation
0 – 9	4 – 8%	Low risk — standard ICU monitoring appropriate
10 – 19	15 – 25%	Moderate risk — close monitoring, active intervention
20 – 29	40 – 55%	High risk — aggressive supportive care
30 – 34	~75%	Critical — maximum support, consider goals of care
Above 35	~85%	Extremely critical — goals of care discussion essential

How to Use This APACHE II Calculator

Enter Acute Physiological Variables: For each of the 12 variables, select the category that corresponds to the patient's worst value within the first 24 hours of ICU admission.
Enter Glasgow Coma Scale: Select the GCS (3-15). The calculator automatically applies the formula: GCS Points = 15 - GCS, meaning a GCS of 15 adds 0 points while a GCS of 3 adds 12 points.
Select Age Range: Choose the patient's age category.
Select Chronic Health Status: Indicate whether the patient has severe organ insufficiency or is immunocompromised, and whether surgery was elective or emergency.
Review Total Score and Mortality Estimate: The calculator sums all points and provides a predicted mortality percentage with clinical interpretation.

Worked Examples

Moderate Severity ICU Patient

Problem:

A 62-year-old patient with community-acquired pneumonia on day 1: temp 38.6°C, MAP 65, HR 110, RR 28, PaO2 60 on FiO2 0.40, pH 7.31, Na 135, K 3.8, Cr 1.2, Hct 34%, WBC 18, GCS 14. No chronic organ failure.

Solution Steps:

1Temp (38.6): 1 pt; MAP (65): 2 pts; HR (110): 2 pts; RR (28): 1 pt; Oxygenation (PaO2 60): 0 pts
2pH (7.31): 2 pts; Na (135): 0 pts; K (3.8): 0 pts; Cr (1.2): 0 pts; Hct (34): 0 pts; WBC (18): 1 pt
3GCS: 15-14 = 1 pt. Total physiology: 10 pts
4Age 62 (55-64): 3 pts. Chronic health: 0 pts
5Total APACHE II: 10 + 3 + 0 = 13

Result:

APACHE II = 13 (~15% predicted mortality). This is in the moderate risk range. The patient requires close ICU monitoring and active treatment, but the prognosis is favorable with appropriate care.

Tips & Best Practices

✓Use the worst value within the first 24 ICU hours for each variable — not the admission value
✓APACHE II was validated on day-1 ICU values; it is not designed for serial recalculation during the ICU stay
✓Always interpret APACHE II as a population-level risk estimate, not an individual prediction

Frequently Asked Questions

APACHE II is calculated using the most deranged physiological values from the first 24 hours of ICU admission. It should not be calculated later in the ICU stay for mortality prediction because it was validated on day-1 data. Serial APACHE scores beyond day 1 are not validated for mortality prediction but may be used in research to track physiological trajectory.

APACHE II has several limitations: it was developed on 1980s US ICU populations and may overestimate mortality in modern ICUs; it excludes surgical diagnosis categories; it does not account for the primary admission diagnosis (unlike APACHE IV); and it was not designed to predict individual patient mortality — it works best for group-level benchmarking. Modern ICUs increasingly use APACHE IV, SAPS 3, or SOFA scores alongside APACHE II.

Sources & References

Last updated: 2026-06-06

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Sources

•World Health Organization (WHO) — Global health metrics, disease classification, and nutritional standards. who.int
•Centers for Disease Control and Prevention (CDC) — Health statistics, BMI guidelines, and disease prevention data. cdc.gov
•National Institutes of Health (NIH) — Medical research, clinical guidelines, and health calculators. nih.gov
•Mayo Clinic — Clinical health information, disease reference, and wellness guidance. mayoclinic.org

For a complete list of all references used across the site, visit our full sources page.

Editorial Note

MyCalcBuddy Editorial Team

This page is maintained as an educational calculator reference.

Source

Formula Source: WHO Health Metrics Standards

by World Health Organization

UpdatedLast reviewed: May 2026

CheckedFormula checks are based on standard references and internal QA review.