41: Are We Relying on Proper Pain Assessment? Exploring the Rat Grimace Scale�s Potential

Topic: Basic Science
Subtopic: Non-specific to any diagnosis (including studies in healthy animals), Assessment and Measurement of Pain/Nociception, Behavioral studies

Background and Aims: Recognizing pain in laboratory animals is crucial for valid interpretations of preclinical pain models. The Rat Grimace Scale (RGS), based on scoring facial expressions, presents itself as an objective and non-evoked method for measurement of pain. Although it is validated for use in acute pain models for up to 48 hours, it is often used outside this timeframe and in chronic and neuropathic models. Applying the RGS in unvalidated contexts may allow pain being undetected which could affect our results. We investigated whether the scale remains reliable beyond its established limits of time and pain types.

Methods: By systematically reviewing studies that employed the RGS in preclinical pain and animal welfare research, we characterized the use of the scale across models that induce pain. To examine its accuracy over time and across pain types, we compared the reported RGS outcomes with findings from established behavioral pain assays, assessing the agreement between measures. This comparison allowed us to evaluate whether the RGS provides a reliable means of detecting pain in longer-term pain as well as neuropathic models.

Results: This review showed extensive use of the RGS well beyond its validated timeframe and across pain types that were not part of its original development. The broad, and often unstandardized, application reflects the wider adoption of the method despite its unclear accuracy outside a narrow set of conditions. By exploring the RGS’s sensitivity and accuracy (concordance with other measures of pain) over time and across models of varying severity, we aim to convey the uses - and the limits - of this method.

Conclusions: The RGS is currently being used beyond its original scope. Accurate pain assessment is essential for drawing reliable conclusions in this research field – when pain is inaccurately measured, data interpretation and, in extend of that, translation to clinical studies may be compromised. Unrecognized or poorly managed pain weakens confidence in experimental findings and diminishes animal welfare, leading to compromised research integrity and unnecessary suffering. Clarifying when the Rat Grimace Scale provides reliable information may help improve pain assessment and welfare monitoring, while supporting both animal welfare and the credibility of preclinical research.

References: 1. Sotocinal SG, Sorge RE, Zaloum A, et al. The Rat Grimace Scale: A Partially Automated Method for Quantifying Pain in the Laboratory Rat via Facial Expressions. Molecular Pain. 2011;7. doi:10.1186/1744-8069-7-55

Presenting Author: Helene Dragelund Garcia
Submitting Author: Helene Dragelund Garcia

Senior Author: Otto Kalliokoski

IASP 2026 Global Year theme of Neuropathic Pain: Yes

• Sara Hestehave - Department of Veterinary and Animal Sciences, University of Copenhagen
• Otto Kalliokoski - Department of Veterinary and Animal Sciences, University of Copenhagen