Generation of de novo reference values for the thyroid hormones TT4, fT4 and TSH in healthy pet rabbits (Oryctolagus cuniculus) and healthy pet guinea pigs (Cavia porcellus) in conjunction with a TRH-stimulation test

Abstract

In rabbits and guinea pigs, total thyroxine (TT4) and free thyroxine (fT4) reference values have been previously published. However, most studies have been performed on laboratory animals with small sample sizes. A reference value for thyroid-stimulating hormone (TSH) measurement has not yet been established for either species. With the increasing popularity of pet guinea pigs and rabbits in veterinary practice, established reference values are needed to make a diagnosis and promptly initiate appropriate treatment. Plasma samples from a healthy and defined animal population of 41 pet rabbits (n = 41 TT4, fT4, TSH) and 73 pet guinea pigs (n = 73 TT4 and fT4; n = 51 TSH) were evaluated using chemiluminescence assay (CLIA; for TT4, fT4) and enzyme-linked immunosorbent assay (ELISA; for TSH) to establish reference values. A thyrotropin teleasing hormone (TRH)-stimulation test (n = 4; for each species) was conducted to validate the TSH ELISA test kits. Range, mean, median, standard deviation, interquartile range, 95% reference interval, and 90% confidence intervals for lower and upper reference limits of TT4, fT4, and TSH in healthy pet guinea pigs and healthy pet rabbits were assessed. In addition, the influence of age, sex, and housing on TT4, fT4, and TSH levels was investigated. In this study, TSH reference values were established in pet rabbits and guinea pigs for the first time. Reference values for both TT4 and fT4 were also established de novo for both species. Only with evidence- and population-based reference values can thyroid diseases be precisely and correctly diagnosed to prevent inadequate treatment.