Feline Grimace Scale (FGS)

Overview

Developer

Evangelista, Watanabe, Leung, Monteiro, O'Toole, Pang, Steagall — Université de Montréal

Year published

2019

Species

Feline

Domain

Acute pain

Structure and administration

5 facial action units (ear position, orbital tightening, muzzle tension, whisker change, head position) each scored 0-2. Total 0-10; published clinical threshold is normalised >= 0.39 (raw >= 4).

Owner- or clinician-completed via reference-photo matching, 2-3 minutes per assessment.

Psychometric properties

Cronbach α

0.89

Test-retest ICC

0.85

Cut-off and interpretation

Cut-off threshold

5

Source: Evangelista et al. 2019 publishes a normalised threshold of 0.39 (raw >= 4) as analgesia-indicated. Sightline shifts the 'consult vet' band to raw >= 5 to reduce false-positive escalation in owner-completed assessments while preserving the borderline 3-4 range as a re-score prompt.

Citation and validation

Evangelista MC, Watanabe R, Leung VSY, Monteiro BP, O'Toole E, Pang DSJ, Steagall PV. Facial expressions of pain in cats: the development and validation of a Feline Grimace Scale. Sci Rep 2019;9:19128.

DOI: 10.1038/s41598-019-55693-8

Revisions

• v1.0 (Evangelista et al. 2019) — original five-unit scale validated against acute clinical and post-procedure pain. Reference imagery and online scoring tool published at felinegrimacescale.com under CC-BY 4.0.
• Cross-cultural validation (Steagall et al., subsequent publications) — confirmed psychometric performance across populations and observers.

Target population

Cats with acute or post-procedural pain. Specifically validated for clinical and post-operative pain detection. Brachycephalic breeds (Persian, Himalayan, Exotic Shorthair, British Shorthair, Scottish Fold) can score artificially high because resting facial morphology overlaps the AU patterns the scale flags; Sightline surfaces a warning before the questionnaire starts and recommends cross-referencing with FMPI-SF or asking the vet to score in person.

Available languages

English (UK)

Licence

Reference imagery is CC-BY 4.0 via felinegrimacescale.com. The instrument is free for non-commercial use; commercial deployment requires a licence agreement before public launch.

Scoring algorithm version

sightline-fgs-v1.0.0

Strengths

• Fast (2-3 minutes), suitable for both owner-side post-procedure tracking and clinician bedside use.
• Strong psychometrics (Cronbach α 0.89, test-retest ICC 0.85) for an observer-rated scale.
• Reference imagery is CC-BY 4.0, so Sightline can carry the photos in-app once the assets are sourced and attributed.
• The published clinical cutoff (analgesia indicated at normalised >= 0.39) is one of the few cat-specific pain thresholds with population-validation data.

Limitations

• Brachycephalic cats (flat-faced breeds) are a known false-positive group; Sightline shows a warning and recommends cross-referencing with FMPI-SF.
• The scoring is observer-rated, so inter-rater reliability depends on owner familiarity with the reference photos.
• FGS scores can be elevated by stress, restraint, or unfamiliar environments; in-clinic scoring within 5-10 minutes of a settled cat is more reliable than freshly-handled scoring.
• The reference imagery sits behind a CC-BY 4.0 licence; commercial deployment requires confirmation of attribution wording with the rights holder before public launch.

Why Sightline uses it

FGS is the only widely-validated owner-administered acute pain instrument for cats. Pairing FGS (acute, point-in-time) with FMPI-SF (chronic, longitudinal) and CSOM (owner-defined) gives Sightline a comprehensive cat-pain coverage. The CC-BY 4.0 reference imagery means Sightline can ship a fully-functional in-app scoring tool without per-deployment licence fees, once the assets are sourced and attributed correctly.