Reliability and construct validity of a composite pain scale for rabbit (CANCRS) in a clinical environment

A composite pain scale for assessing and quantifying pain in rabbits (CANCRS) has been designed merging the Rabbit Grimace Scale (RbtGS) and a scale including clinical parameters (CPS). Construct validity and inter-rater reliability were assessed for CANCRS, for RbtGS and for CPS, in order to test their potential to detect pain in a clinical setting. Rabbits (n = 116) were either hybrids or purebreds and they were independently evaluated by two raters, who could be veterinarians (V) or veterinary medicine students (S). Score intervals determined four pain classes (No pain, Discomfort, Moderate pain and Severe pain) that matched presumptive pain classes associated with some pathological conditions. A chi-square test was used to assess the construct validity of the scales by checking how frequently scale results and presumptive pain classes matched. Sixty-nine patients were evaluated by one V and one S, whereas forty-seven rabbits were assessed by two V, in order to test inter-rater reliability. An intra-class correlation coefficient (ICC) was used to test reliability of the scales, whereas Cohen's kappa tested inter-rater agreement for each parameter of the CANCRS. Construct validity results show that CANCRS and RbtGS efficiently reveal pain (P ≤ 0.05), while CPS does not (p > 0.05). Inter-rater reliability was very good for both CANCRS and CPS (ICC 0.88 V-V, 0.94 between V-S; ICC 0.97 V-V, 0.91 V-S) and good for RbtGS (ICC 0.77 V-V, 0.88 V-S); therefore, CPS reproducibility was better between veterinarians and students than between veterinarians. Inter-rater agreement between veterinarians and veterinary medicine students was moderate to very good for all the parameters included in the CANCRS (Cohen's kappa >0,60). In conclusion, it is possible to state that the CANCRS has construct validity and it is a reliable tool for use in clinical practice, when coping with many rabbits with morphological differences. It is easy and fast to use and enriches the RbtGS with some clinical parameters that should be monitored during any clinical examination, allowing for capture of the multidimensional aspect of pain.