APACHE II Score Calculator — ICU Severity
The APACHE II (Acute Physiology and Chronic Health Evaluation II) score combines 12 physiological measurements, patient age, and chronic health status into a 0–71 score. It is used in ICUs worldwide to quantify illness severity and estimate hospital mortality risk.
°C
mmHg
bpm
breaths/min
mmHg
mmHg
mEq/L
mEq/L
mg/dL
Acute Renal Failure
%
×10³/mm³
Glasgow Coma Scale (GCS)
years
Chronic Health Status
Range 0–71: higher scores indicate greater severity and mortality risk
- 1
Acute Physiology Score (APS)
012 variables (temp, MAP, HR, RR, oxygenation, pH, Na, K, Cr, Hct, WBC, GCS) each scored 0–4 for deviation from normal; GCS component = 15 − GCS. - 2
Age points
2 - 3
Chronic health points
0 - 4
APACHE II score
0 + 2 + 0 = 2
How does this calculator work?
APACHE II = APS (12 physiological variables scored 0–4 each, worst value in first 24 h) + age points (0–6) + chronic health points (0/2/5). Total range: 0–71. Predicted mortality is calculated via ln(R/1−R) = −3.517 + score×0.146. This base formula does not include a diagnosis-specific term from the full model.
Formula
How this is calculated
APACHE II was developed by Knaus et al. (1985) and remains one of the most widely validated ICU severity scores. It has three components. The Acute Physiology Score (APS) sums points from 12 physiological variables — temperature, mean arterial pressure, heart rate, respiratory rate, oxygenation, arterial pH, serum sodium, potassium, creatinine (doubled in acute renal failure), hematocrit, white blood cell count, and a GCS-derived score (15 minus the actual GCS) — each scored 0–4 based on deviation from a normal range, giving a possible APS of 0–60. Age adds 0–6 points on a stepped scale starting at age 45. Chronic health adds 0, 2, or 5 points depending on whether the patient has a severe organ insufficiency and whether they were admitted electively or as an emergency.
The predicted hospital mortality uses the logistic regression formula published in the original paper: ln(R/1−R) = −3.517 + (APACHE II × 0.146), giving a probability R. This base formula applies to non-surgical medical ICU patients and does not include a diagnosis-specific coefficient; the full model adds a disease category term (available in the original publication) that typically shifts the estimate by ±10–20 percentage points depending on condition.
Limitations: APACHE II should use the worst value recorded in the first 24 hours of ICU admission — not admission values — and trained clinical staff must determine the scores. The model was calibrated on 1980s US ICU populations; local mortality may differ significantly. APACHE II should never be used as the sole criterion for withholding or withdrawing treatment.
Frequently asked questions
An APACHE II score of 25 or above carries a predicted hospital mortality of roughly 50–75% in the original non-surgical medical ICU cohort. Scores below 10 correspond to roughly <10% predicted mortality. However, the actual mortality in any individual patient depends on diagnosis, treatment response, and local ICU capabilities.
The original protocol specifies the worst (most abnormal) value observed in the first 24 hours of ICU admission for each parameter. If a value is not available (e.g. no arterial blood gas), some institutions substitute zero points; others use the last available value. Document your assumption.
The APACHE II scoring table specifies that the creatinine APS score is multiplied by 2 if the patient has acute renal failure. This reflects the added severity of acute kidney injury on top of the biochemical abnormality itself, and it was an empirical finding from the original dataset.
Also known as
TG we-Calculate Editorial Team. (2026). APACHE II Score Calculator — ICU Severity [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/apache-ii-calculator
TG we-Calculate Editorial Team. "APACHE II Score Calculator — ICU Severity." TG we-Calculate. 2026. https://we-calculate.com/calculator/apache-ii-calculator.
TG we-Calculate Editorial Team, "APACHE II Score Calculator — ICU Severity," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/apache-ii-calculator
@misc{wecalculate_apache_ii_calculator, title = {APACHE II Score Calculator — ICU Severity}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/apache-ii-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?