APACHE II Calculator — ICU Mortality Risk Score

Q: What are the three components of the APACHE II score?

APACHE II sums three parts: the Acute Physiology Score (12 physiologic variables measured in the first 24 hours, each scored 0–4), Age points (0 to 6), and Chronic Health points (0, 2, or 5 for severe organ insufficiency or an immunocompromised state, depending on admission type). The total ranges from 0 to 71.

Q: What is the range of the APACHE II score?

The theoretical range is 0 to 71 — up to 60 from the 12 acute physiology variables (including a doubled creatinine for acute kidney injury), up to 6 for age, and up to 5 for chronic health. In practice, survivable scores rarely exceed the mid-50s. Higher scores indicate greater severity of illness and higher predicted hospital mortality.

Q: How are the chronic health points assigned?

Chronic health points apply only when the patient has a history of severe organ insufficiency (e.g., cirrhosis, NYHA class IV heart failure, severe COPD, dialysis) or is immunocompromised. If that history is present, add 5 points for a nonoperative or emergency postoperative admission, or 2 points for an elective postoperative admission. Patients without such a history score 0.

Q: How does the Glasgow Coma Scale contribute to APACHE II?

The neurologic points equal 15 minus the actual Glasgow Coma Scale score. A fully alert patient (GCS 15) contributes 0 points, while a deeply comatose patient (GCS 3) contributes 12 points. If the patient is sedated, clinicians typically use the estimated pre-sedation GCS.

Q: How is APACHE II different from the SOFA score?

APACHE II is a one-time severity-of-illness score calculated from the worst values in the first 24 hours of ICU admission, primarily to estimate mortality risk. SOFA (Sequential Organ Failure Assessment) is a lighter six-organ score designed to be repeated daily to track the evolution of organ dysfunction over time. They answer different questions — initial severity versus trajectory.

Q: Why does this tool give an approximate mortality range rather than an exact percentage?

The validated APACHE II mortality equation adds a weight specific to the patient's admission diagnostic category (for example, sepsis versus trauma versus post-CABG), which a general-purpose calculator cannot reproduce faithfully. This tool therefore reports the published Knaus 1985 death-rate bands for nonoperative and postoperative patients as an approximate reference range only — never a precise per-patient prediction.

APACHE II Score	Nonoperative	Postoperative
0–4	~4%	~1%
5–9	~8%	~3%
10–14	~15%	~7%
15–19	~25%	~12%
20–24	~40%	~30%
25–29	~55%	~35%
30–34	~75%	~73%
≥ 35	~85%	~88%

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Walk-through

How to Use This Calculator

3 steps

1

Enter the 12 acute physiology variables

Type the worst value recorded in the first 24 hours of ICU admission for temperature, mean arterial pressure, heart rate, respiratory rate, oxygenation, arterial pH, sodium, potassium, creatinine, hematocrit, white blood cell count, and the Glasgow Coma Scale. For oxygenation, choose A–aDO₂ when FiO₂ is 0.5 or higher, or PaO₂ when FiO₂ is below 0.5. Check the acute kidney injury box to double the creatinine points. Every field starts at a normal (0-point) value, so only abnormal entries raise the score.

2

Add age and chronic health status

Enter the patient's age and choose the chronic health option. Chronic health points apply only with a history of severe organ insufficiency (cirrhosis, NYHA class IV heart failure, severe COPD, dialysis) or immunocompromise: add 5 for a nonoperative or emergency postoperative admission, or 2 for an elective postoperative admission. Age is the only required field.

3

Read the score, tier, and component breakdown

The result card shows the total APACHE II score (0–71), the risk tier, and the approximate hospital mortality for nonoperative and postoperative patients. Open the Component Breakdown tab to see the acute-physiology / age / chronic-health split and how many points each variable contributed, and the Mortality Estimate tab for the full reference band table.

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Reference

Formula & Methodology

15 formulas

Total APACHE II score

APACHE II = Acute Physiology Score + Age points + Chronic Health points

The score sums three components. The Acute Physiology Score adds the points from 12 variables (each 0–4, worst value in the first 24 hours); age contributes 0–6; chronic health contributes 0, 2, or 5. The theoretical maximum is 71. Higher scores indicate greater severity of illness and higher predicted mortality.

Temperature (°C) points

≥41: 4 | 39–40.9: 3 | 38.5–38.9: 1 | 36–38.4: 0 | 34–35.9: 1 | 32–33.9: 2 | 30–31.9: 3 | ≤29.9: 4

Core (rectal) temperature. Both hyperthermia and hypothermia add points; 36–38.4 °C is the 0-point band.

Mean arterial pressure (mmHg) points

≥160: 4 | 130–159: 3 | 110–129: 2 | 70–109: 0 | 50–69: 2 | ≤49: 4

MAP = (systolic + 2 × diastolic) / 3. Both hypertension and hypotension add points.

Heart rate (bpm) points

≥180: 4 | 140–179: 3 | 110–139: 2 | 70–109: 0 | 55–69: 2 | 40–54: 3 | ≤39: 4

Ventricular response rate. Both tachycardia and bradycardia add points.

Respiratory rate (/min) points

≥50: 4 | 35–49: 3 | 25–34: 1 | 12–24: 0 | 10–11: 1 | 6–9: 2 | ≤5: 4

Ventilated or spontaneous breaths per minute.

Oxygenation points

FiO₂ ≥ 0.5 → A–aDO₂: ≥500: 4 | 350–499: 3 | 200–349: 2 | <200: 0 | FiO₂ < 0.5 → PaO₂: >70: 0 | 61–70: 1 | 55–60: 3 | <55: 4

Use the alveolar–arterial oxygen gradient (A–aDO₂) when the inspired oxygen fraction is 0.5 or higher; otherwise use PaO₂ in mmHg.

Arterial pH points

≥7.7: 4 | 7.6–7.69: 3 | 7.5–7.59: 1 | 7.33–7.49: 0 | 7.25–7.32: 2 | 7.15–7.24: 3 | <7.15: 4

Arterial pH from a blood gas. If no arterial gas is available, the original score allows a serum bicarbonate substitute, which this tool does not implement.

Serum sodium (mmol/L) points

≥180: 4 | 160–179: 3 | 155–159: 2 | 150–154: 1 | 130–149: 0 | 120–129: 2 | 111–119: 3 | ≤110: 4

Both hypernatremia and hyponatremia add points.

Serum potassium (mmol/L) points

≥7: 4 | 6–6.9: 3 | 5.5–5.9: 1 | 3.5–5.4: 0 | 3–3.4: 1 | 2.5–2.9: 2 | <2.5: 4

Both hyperkalemia and hypokalemia add points.

Serum creatinine (mg/dL) points

≥3.5: 4 | 2–3.4: 3 | 1.5–1.9: 2 | 0.6–1.4: 0 | <0.6: 2 (points DOUBLED for acute kidney injury)

Creatinine points are doubled when acute kidney injury is present, so the maximum contribution is 8 points.

Hematocrit (%) points

≥60: 4 | 50–59.9: 2 | 46–49.9: 1 | 30–45.9: 0 | 20–29.9: 2 | <20: 4

Both polycythemia and anemia add points.

White blood cell count (×10³/µL) points

≥40: 4 | 20–39.9: 2 | 15–19.9: 1 | 3–14.9: 0 | 1–2.9: 2 | <1: 4

Both leukocytosis and leukopenia add points.

Glasgow Coma Scale points

GCS points = 15 − actual GCS (range 0–12)

A fully alert patient (GCS 15) scores 0; a deeply comatose patient (GCS 3) scores 12. Use the estimated pre-sedation GCS when the patient is sedated.

Age points

≤44: 0 | 45–54: 2 | 55–64: 3 | 65–74: 5 | ≥75: 6

Older age independently raises predicted mortality.

Chronic health points

None: 0 | Elective postoperative (+ severe insufficiency / immunocompromise): 2 | Nonoperative or emergency postoperative (+ severe insufficiency / immunocompromise): 5

Points apply only with a documented history of severe organ insufficiency or an immunocompromised state; the value depends on the admission type.

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High YMYL

Trust, Methodology & Sources

Reviewed by Calculover Editorial Review · Updated 2026-07-22 · 3 sources

Editorial accountability

Author: Quinn Sumner - Editor

Owner: Quinn Sumner - Editorial owner

Reviewer: Calculover Editorial Review - Clinical-source review

Last reviewed: 2026-07-22

Last verified: 2026-07-22

Data effective: 2026-07-22

Methodology

The calculator implements the original APACHE II model (Knaus et al., Crit Care Med 1985): it sums the Acute Physiology Score (12 variables, each 0–4, worst value in the first 24 hours), age points (0–6), and chronic health points (0/2/5), for a total of 0–71. Every tier cutoff was cross-verified digit-for-digit against the Merck Manual Professional Edition reproduction of the original Knaus 1985 table. The Glasgow Coma Scale contributes 15 minus the actual GCS, and creatinine points are doubled for acute kidney injury.

Assumption: Each variable uses the worst value recorded in the first 24 hours of ICU admission; blank physiology fields are treated as normal (0 points).

Assumption: Oxygenation uses the A–aDO₂ gradient when FiO₂ is 0.5 or higher and PaO₂ when FiO₂ is below 0.5; creatinine is entered in mg/dL.

Assumption: Chronic health points apply only with a documented history of severe organ insufficiency or immunocompromise.

Limitations & guidance

Mortality is reported only as an approximate reference range from the Knaus 1985 death-rate bands; the validated equation adds a diagnostic-category coefficient that cannot be faithfully reproduced in a general tool, so the figures are not a per-patient prediction.

APACHE II is a one-time first-24-hour score, not a daily trend tool, and predates many modern critical-care therapies.

The score must not be the sole basis of any individual treatment, triage, or withdrawal-of-care decision; it supports, but does not replace, full clinical assessment.

Professional guidance: This calculator is for education and clinical decision support only and is not medical advice, diagnosis, or treatment. APACHE II scores support, but do not replace, the judgment of a licensed clinician and local ICU protocols; treatment decisions require full clinical assessment.

Primary sources

APACHE II: a severity of disease classification system - Knaus WA, Draper EA, Wagner DP, Zimmerman JE. Critical Care Medicine, 1985;13(10):818-829

APACHE II Score Calculator - MDCalc

APACHE II Scoring System (table) - Merck Manual Professional Edition

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Glossary

Key Terms Explained

9 terms

APACHE II Acute Physiology and Chronic Health Evaluation II — a severity-of-illness score (Knaus 1985) that estimates ICU mortality risk from acute physiology, age, and chronic health, ranging 0 to 71.

Acute Physiology Score (APS) The sum of points from the 12 acute physiology variables, each scored 0 to 4 using the worst value recorded in the first 24 hours of ICU admission.

Chronic health points Extra points (2 or 5) added when the patient has a history of severe organ insufficiency or an immunocompromised state, with the value depending on whether the admission was elective postoperative or nonoperative / emergency postoperative.

Glasgow Coma Scale (GCS) A 3-to-15 scale of consciousness. In APACHE II the neurologic points equal 15 minus the actual GCS, so lower consciousness contributes more points.

A–a gradient (A–aDO₂) The alveolar–arterial oxygen difference, used as the oxygenation variable when the inspired oxygen fraction (FiO₂) is 0.5 or higher; PaO₂ is used when FiO₂ is below 0.5.

Elective vs emergency admission Elective postoperative admissions are planned after scheduled surgery; nonoperative and emergency postoperative admissions are unplanned. The distinction changes the chronic health points and the mortality reference column.

Immunocompromise A state of reduced immune function (e.g., from chemotherapy, high-dose steroids, or an immunosuppressive disease) that qualifies a patient for chronic health points.

ICU severity score A numeric summary of how critically ill a patient is on ICU admission, used to compare illness severity, benchmark units, and estimate expected mortality.

Mortality prediction An estimate of the probability of hospital death. The validated APACHE II equation adds a diagnostic-category coefficient; this tool reports the published death-rate bands as an approximate reference range instead.

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Scenarios

Real-World Examples

3 worked examples

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Low score

52-year-old, stable medical admission

Vitals & labs all within normal (0-point) ranges GCS 15 Age 52 yr Chronic health none

All 12 physiology variables are normal (Acute Physiology Score 0). Age 52 adds 2 points and there are no chronic health points, so the total APACHE II score is 2 — the low-risk tier, with an approximate hospital mortality near 4% (nonoperative) or 1% (postoperative). Interpret alongside the full clinical picture.

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Moderate score

64-year-old with a systemic illness

Temp / MAP / HR / RR 38.7 °C / 62 / 116 / 26 PaO₂ / pH 66 mmHg / 7.31 Na / K / Creatinine 128 / 5.6 / 1.7 mg/dL Hct / WBC / GCS 44% / 16 / 14 Age / Chronic health 64 yr / none

The physiology derangements sum to an Acute Physiology Score of 16 (temp 1, MAP 2, HR 2, RR 1, oxygenation 1, pH 2, sodium 2, potassium 1, creatinine 2, hematocrit 0, WBC 1, GCS 1). Age 64 adds 3, for a total of 19 — the moderate tier, with an approximate hospital mortality near 25% (nonoperative) or 12% (postoperative).

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High score

74-year-old with septic shock and acute kidney injury

Temp / MAP / HR / RR 39.5 °C / 55 / 145 / 36 A–aDO₂ / pH 260 (FiO₂ ≥ 0.5) / 7.22 Na / K / Creatinine 128 / 5.7 / 2.6 mg/dL (AKI ×2) Hct / WBC / GCS 29% / 22 / 10 Age / Chronic health 74 yr / nonoperative + immunocompromise (+5)

Severe multi-system derangement drives the Acute Physiology Score to 34, including a doubled creatinine (6 points) for acute kidney injury. Age 74 adds 5 and chronic health adds 5, for a total of 44 — the very-high-risk tier, with an approximate hospital mortality near 85% (nonoperative) or 88% (postoperative). This is an approximate reference only, not a per-patient prediction.

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Deep Dive

Understanding the APACHE II Score

3 chapters · 5 min read

The APACHE II score turns a snapshot of a patient's first 24 hours in intensive care into a single number that reflects how critically ill they are. Developed by Knaus and colleagues in 1985, it remains one of the most widely used severity-of-illness scores in critical care — for estimating mortality risk, comparing case mix between units, and stratifying patients in research.

How the APACHE II score works

APACHE II adds three parts. The Acute Physiology Score takes the worst value in the first 24 hours for 12 variables — temperature, mean arterial pressure, heart rate, respiratory rate, oxygenation, arterial pH, sodium, potassium, creatinine, hematocrit, white blood cell count, and the Glasgow Coma Scale — and scores each from 0 (normal) to 4 (extreme derangement). Age points add 0 to 6, and chronic health points add 2 or 5 when a patient has severe long-standing organ disease or an immunocompromised state. The three parts sum to a total from 0 to 71.

Two variables have special rules. The neurologic contribution is 15 minus the actual Glasgow Coma Scale, so a comatose patient contributes up to 12 points. And creatinine points are doubled when acute kidney injury is present, up to 8 points.

From score to mortality — and why it is approximate here

In the original study, a higher APACHE II score tracked closely with higher hospital mortality. The published death-rate table shows roughly 4% mortality at a score of 0–4 rising to about 85% at 35 or above for nonoperative patients, with lower rates for postoperative patients. This calculator reports those bands as an approximate reference range.

The fully validated APACHE II mortality equation is more specific: it adds a coefficient for the patient's admission diagnostic category (for example, sepsis, trauma, or post-CABG) on top of the score. That per-diagnosis weight cannot be reproduced faithfully in a general-purpose tool, so the numbers here should be read as a reference range rather than a precise per-patient prediction.

How it is used and its limits

APACHE II is a one-time score anchored to the first 24 hours; it is not designed to be recalculated daily like the SOFA score, which tracks organ dysfunction over time. It describes a population's expected mortality well but should never be used to make an individual treatment or withdrawal-of-care decision on its own. It also predates many modern therapies, does not capture frailty or specific diagnoses beyond the diagnostic-category weight, and depends on complete, accurate first-24-hour data. Treat the output as one input among many in a full clinical assessment.

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Questions

Frequently Asked Questions

6 questions

What are the three components of the APACHE II score?+

APACHE II sums three parts: the Acute Physiology Score (12 physiologic variables measured in the first 24 hours, each scored 0–4), Age points (0 to 6), and Chronic Health points (0, 2, or 5 for severe organ insufficiency or an immunocompromised state, depending on admission type). The total ranges from 0 to 71.

What is the range of the APACHE II score?+

The theoretical range is 0 to 71 — up to 60 from the 12 acute physiology variables (including a doubled creatinine for acute kidney injury), up to 6 for age, and up to 5 for chronic health. In practice, survivable scores rarely exceed the mid-50s. Higher scores indicate greater severity of illness and higher predicted hospital mortality.

How are the chronic health points assigned?+

Chronic health points apply only when the patient has a history of severe organ insufficiency (e.g., cirrhosis, NYHA class IV heart failure, severe COPD, dialysis) or is immunocompromised. If that history is present, add 5 points for a nonoperative or emergency postoperative admission, or 2 points for an elective postoperative admission. Patients without such a history score 0.

How does the Glasgow Coma Scale contribute to APACHE II?+

The neurologic points equal 15 minus the actual Glasgow Coma Scale score. A fully alert patient (GCS 15) contributes 0 points, while a deeply comatose patient (GCS 3) contributes 12 points. If the patient is sedated, clinicians typically use the estimated pre-sedation GCS.

How is APACHE II different from the SOFA score?+

APACHE II is a one-time severity-of-illness score calculated from the worst values in the first 24 hours of ICU admission, primarily to estimate mortality risk. SOFA (Sequential Organ Failure Assessment) is a lighter six-organ score designed to be repeated daily to track the evolution of organ dysfunction over time. They answer different questions — initial severity versus trajectory.

Why does this tool give an approximate mortality range rather than an exact percentage?+

The validated APACHE II mortality equation adds a weight specific to the patient's admission diagnostic category (for example, sepsis versus trauma versus post-CABG), which a general-purpose calculator cannot reproduce faithfully. This tool therefore reports the published Knaus 1985 death-rate bands for nonoperative and postoperative patients as an approximate reference range only — never a precise per-patient prediction.

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APACHE II Score Calculator

Acute Physiology — worst values, first 24 h

Age & Chronic Health

APACHE II Score & Mortality

Score Components

Per-Variable Point Breakdown

Approximate Hospital Mortality by Score

How to Use This Calculator

Enter the 12 acute physiology variables

Add age and chronic health status

Read the score, tier, and component breakdown

Formula & Methodology

Trust, Methodology & Sources

Key Terms Explained

Real-World Examples

Low score

Moderate score

High score

Understanding the APACHE II Score

How the APACHE II score works

From score to mortality — and why it is approximate here

How it is used and its limits

Frequently Asked Questions

Get a branded PDF of your results

APACHE II Score Calculator

Acute Physiology — worst values, first 24 h

Age & Chronic Health

APACHE II Score & Mortality

Score Components

Per-Variable Point Breakdown

Approximate Hospital Mortality by Score

How to Use This Calculator

Enter the 12 acute physiology variables

Add age and chronic health status

Read the score, tier, and component breakdown

Formula & Methodology

Trust, Methodology & Sources

Key Terms Explained

Real-World Examples

Understanding the APACHE II Score

How the APACHE II score works

From score to mortality — and why it is approximate here

How it is used and its limits

Frequently Asked Questions

Get a branded PDF of your results

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