Facial expressions of pain have been identified in several animal species. The aim of this systematic review was to provide evidence on the measurement properties of grimace scales for pain assessment. The protocol was registered (SyRF#21-November-2019), and the study is reported according to the PRISMA guidelines. Studies reporting the development, validation, and the assessment of measurement properties of grimace scales were included. Data extraction and assessment were performed by 2 investigators, following the COnsensus-based Standards for the Selection of Health Measurement INstruments guidelines. Six categories of measurement properties were assessed: internal consistency, reliability, measurement error, criterion and construct validity, and responsiveness. Overall strength of evidence (high, moderate, and low) of each instrument was based on methodological quality, number of studies, and studies' findings. Twelve scales for 9 species were included (mice, rats, rabbits, horses, piglets, sheep or lamb, ferrets, cats, and donkeys). Considerable variability regarding their development and measurement properties was observed. The Mouse, Rat, Horse and Feline Grimace Scales exhibited high level of evidence. The Rabbit, Lamb, Piglet and Ferret Grimace Scales and Sheep Pain Facial Expression Scale exhibited moderate level of evidence. The Sheep Grimace Scale, EQUUS-FAP, and EQUUS-Donkey-FAP exhibited low level of evidence for measurement properties. Construct validity was the most reported measurement property. Reliability and other forms of validity have been understudied. This systematic review identified gaps in knowledge on the measurement properties of grimace scales. Further studies should focus on improving psychometric testing, instrument refinement, and the use of grimace scales for pain assessment in nonhuman mammals.

已经在几种动物物种中发现了疼痛的面部表情。本系统评价的目的是为疼痛评估鬼脸量表的测量特性提供证据。该方案已注册（SyRF#21-November-2019），该研究是根据 PRISMA 指南报告的。包括报告鬼脸秤测量特性的开发、验证和评估的研究。数据提取和评估由 2 名研究人员按照基于共识的健康测量仪器选择标准指南进行。评估了六类测量属性：内部一致性、可靠性、测量误差、标准和结构效度以及响应性。整体证据强度（高、中、和低）每种仪器的质量基于方法学质量、研究数量和研究结果。包括 9 个物种的 12 个尺度（小鼠、大鼠、兔子、马、小猪、绵羊或羔羊、雪貂、猫和驴）。观察到关于它们的开发和测量特性的相当大的可变性。老鼠、大鼠、马和猫的鬼脸鳞片展示了高水平的证据。兔子、羔羊、小猪和雪貂鬼脸量表和绵羊疼痛面部表情量表显示出中等水平的证据。Sheep Grimace Scale、EQUUS-FAP 和 EQUUS-Donkey-FAP 显示出低水平的测量特性证据。结构效度是报告最多的测量属性。可靠性和其他形式的有效性尚未得到充分研究。该系统评价确定了鬼脸鳞片测量特性方面的知识空白。进一步的研究应侧重于改进心理测试、仪器改进以及使用鬼脸量表评估非人类哺乳动物的疼痛。