In veterinary research, the visual analog scale (VAS) is commonly used for owner assessment of an animal’s pain. The VAS is a 100-mm line with “no pain” designated as the left end point and “worst possible pain” as the right. This study assessed the validity and reliability of the VAS when used by untrained owners. The dogs used in the study were part of an unrelated clinical trial of 2 new pain treatments using a negative control (placebo) and positive control (carprofen). Only the dogs in these 2 control groups from the clinical trial were used for purposes of this study. Owners evaluated their dogs 4 weeks prior to treatment, at the start of treatment, at weeks 4 and 8 of treatment with carprofen or placebo, and 4 weeks after cessation of treatment (week 12). The VAS was a poor tool for untrained owners because they could not recognize their dogs’ behavior as signs of pain. It was found that owners learned to use the VAS only after discontinuing an effective pain treatment and noting the return of clinical signs.

Commentary: The VAS has been a cornerstone for researchers in evaluating pain control products for dogs. This study indicates that pet owners cannot reliably use this method unless they have been trained to recognize signs of pain in their dogs. On a more clinical note, the fact that pet owners didn’t recognize the signs of pain in their dogs is a concern because pain may go undiagnosed and unmanaged in many patients.—Patricia Thomblison, DVM, MS

Reliability and validity of a visual analogue scale used by owners to measure chronic pain attributable to osteoarthritis in their dogs. Hielm-Björkman AK, Kapatkin AS, Rita HJ. AM J VET RES 72:601-607, 2011.