Classification system

ASA Classification

ASA Physical Status Classification

The ASA Physical Status Classification grades a patient’s pre-operative systemic health from I, a normal healthy patient, to VI, a declared brain-dead organ donor, with an E modifier added for emergency procedures.

No licence required2 items~1 min1–6, lower is better

Physical status

Assign the class that best describes the patient’s systemic health before surgery, independent of the procedure being performed.

1ASA Physical Status class

I — a normal healthy patient1II — a patient with mild systemic disease2III — a patient with severe systemic disease3IV — a patient with severe systemic disease that is a constant threat to life4V — a moribund patient who is not expected to survive without the operation5VI — a declared brain-dead patient whose organs are being removed for donor purposes6

2Is this an emergency procedure?

An emergency is a procedure where delay would significantly increase the threat to life or body part.

No0Yes — add the E modifier1

What the ASA category means

ASA scores run from 1 to 6, where a lower score is better. The bands below are conventional reporting categories, not diagnostic cut-offs.

ASA I1–1
ASA II2–2
ASA III3–3
ASA IV4–4
ASA V–VI5–6

Published criteria and reliability

The published cut-offs that define this instrument, and the measured agreement between observers using it. Each is reported with the population it was derived in.

Type	Value	Subscale	Population	Follow-up	Source
Criterion	ASA III or above is consistently associated with increased perioperative morbidity and mortality	—	Surgical patients across specialties	—	Hackett NJ 2015
Criterion	Interobserver agreement is moderate, with most disagreement between classes II and III	—	Anaesthetists assigning the same patients	—	Sankar A 2014
Criterion	ASA class predicts mortality after hip fracture surgery independently of age	—	Hip fracture	—	Hackett NJ 2015

Criterion is a published cut-off, definition or performance figure belonging to a classification or decision rule — it is not a change score and should not be read as one.

How the score is calculated

Stated in full so the calculation can be independently checked, and reproduced by hand if needed.

The patient is assigned one of six classes describing systemic health before surgery: I, a normal healthy patient; II, a patient with mild systemic disease without substantive functional limitation; III, a patient with severe systemic disease and substantive functional limitation; IV, a patient with severe systemic disease that is a constant threat to life; V, a moribund patient not expected to survive without the operation; and VI, a declared brain-dead patient whose organs are being removed for donation. The letter E is appended for emergency procedures. The classification describes the patient, not the operation.

Instrument profile

Developer: American Society of Anesthesiologists
Institution: American Society of Anesthesiologists
First published: 1941
Custodian: American Society of Anesthesiologists, definitions last revised 2020
Items: 2
Response format: Six-level classification plus an emergency modifier
Score range: 1 to 6
Direction: Lower score = better
Completion time: About 1 minutes
Age range: All ages, with separate paediatric and obstetric examples
Regions: General Health
Conditions: Pre-operative assessment, Perioperative risk, Comorbidity
Procedures: Any surgical procedure
Observer agreement: Interobserver kappa typically 0.2–0.6 depending on whether the ASA examples are used
Validity: Despite its simplicity the classification predicts perioperative mortality, length of stay and complications across a wide range of surgery, which is why it remains embedded in registries and risk models.
Reliability: Agreement is only moderate and improves substantially when assessors use the published examples. The classification is often misapplied by incorporating the surgical procedure or the patient’s age, neither of which is part of the definition.

When to use the ASA

Well suited to

Pre-operative assessment and documentation before any surgical procedure.
Risk adjustment in surgical registries and audit, where it is near-universally recorded.
Communicating overall patient fitness between surgical and anaesthetic teams.

Limitations and poor fits

As a standalone predictor of operative risk, which also depends on the procedure, its urgency and the anaesthetic.
As a substitute for a structured risk calculator when a numerical probability of mortality or complication is needed.
Incorporating age or the surgical procedure into the class — neither is part of the definition.

ASA compared with other instruments

Instruments measuring a related construct, with the practical difference between them.

Instrument	Items	Range	What it adds
CCI	17	0–37	The Charlson Comorbidity Index is a weighted checklist of 16 comorbid conditions that produces a comorbidity score of 0 to 33, to which up to 4 points are added for age, and which estimates 10-year survival at roughly 98% for a total of 0, 90% for 2, 53% for 4 and 21% for 5.
Caprini	37	0–84	The Caprini Risk Assessment Model estimates the risk of venous thromboembolism in a surgical patient by adding risk factors weighted 1, 2, 3 or 5 points — with elective lower limb arthroplasty, a hip, pelvis or leg fracture, stroke and acute spinal cord injury each worth 5 — to give a total that hospital protocols then map to a prophylaxis level.
Wells DVT	10	-2–9	The Wells score for deep vein thrombosis estimates pre-test probability from ten clinical criteria, nine of which add a point and one of which subtracts two, stratifying patients into low, moderate and high probability groups that carry roughly 5%, 17% and 53% prevalence of DVT.

Copyright and permitted use

Published openly because it is the question every clinician and researcher asks before using an instrument, and almost nobody answers it.

No licence requiredRights holder: American Society of Anesthesiologists

The ASA Physical Status Classification and its accompanying examples are published openly by the American Society of Anesthesiologists and are reproduced universally in anaesthetic and surgical practice without a licensing programme.

References

Saklad M. Grading of patients for surgical procedures. Anesthesiology. 1941.
Sankar A, Johnson SR, Beattie WS, Tait G, Wijeysundera DN. Reliability of the American Society of Anesthesiologists physical status scale in clinical practice. British Journal of Anaesthesia. 2014.PMID 24727705
Hackett NJ, De Oliveira GS, Jain UK, Kim JYS. ASA class is a reliable independent predictor of medical complications and mortality following surgery. International Journal of Surgery. 2015.PMID 25728381

Editorial status

This page has not yet been signed off by a named clinical reviewer. The scoring logic is stated in full above so it can be independently verified, and every threshold is traceable to its source. See our editorial methodology.