Reliability of the American Society of Anesthesiologists physical status scale in clinical practice

Br J Anaesth. 2014 Sep;113(3):424-32. doi: 10.1093/bja/aeu100. Epub 2014 Apr 11.


Background: Previous studies, which relied on hypothetical cases and chart reviews, have questioned the inter-rater reliability of the ASA physical status (ASA-PS) scale. We therefore conducted a retrospective cohort study to evaluate its inter-rater reliability and validity in clinical practice.

Methods: The cohort included all adult patients (≥18 yr) who underwent elective non-cardiac surgery at a quaternary-care teaching institution in Toronto, Ontario, Canada, from March 2010 to December 2011. We assessed inter-rater reliability by comparing ASA-PS scores assigned at the preoperative assessment clinic vs the operating theatre. We also assessed the validity of the ASA-PS scale by measuring its association with patients' preoperative characteristics and postoperative outcomes.

Results: The cohort included 10 864 patients, of whom 5.5% were classified as ASA I, 42.0% as ASA II, 46.7% as ASA III, and 5.8% as ASA IV. The ASA-PS score had moderate inter-rater reliability (κ 0.61), with 67.0% of patients (n=7279) being assigned to the same ASA-PS class in the clinic and operating theatre, and 98.6% (n=10 712) of paired assessments being within one class of each other. The ASA-PS scale was correlated with patients' age (Spearman's ρ, 0.23), Charlson comorbidity index (ρ=0.24), revised cardiac risk index (ρ=0.40), and hospital length of stay (ρ=0.16). It had moderate ability to predict in-hospital mortality (receiver-operating characteristic curve area 0.69) and cardiac complications (receiver-operating characteristic curve area 0.70).

Conclusions: Consistent with its inherent subjectivity, the ASA-PS scale has moderate inter-rater reliability in clinical practice. It also demonstrates validity as a marker of patients' preoperative health status.

Keywords: anaesthesiology; health status; reliability and validity.

Publication types

  • Research Support, Non-U.S. Gov't
  • Validation Study

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Anesthesiology*
  • Cohort Studies
  • Female
  • Health Status Indicators*
  • Health Status*
  • Hospital Mortality
  • Humans
  • Length of Stay / statistics & numerical data
  • Male
  • Middle Aged
  • Observer Variation
  • Ontario
  • Psychometrics
  • Reproducibility of Results
  • Retrospective Studies
  • Societies, Medical / standards*
  • Surveys and Questionnaires
  • United States
  • Young Adult