Serum Total Thyroxine Concentrations in Clinically Healthy Pet Rabbits

In small animals, serum total thyroxine concentration (TT₄) is an important parameter used to assess thyroid function in patients. In rabbits, no information is available on the prevalence of thyroid disease and its diagnosis by laboratory methods. The aim of this study was to establish a device- and method-specific reference interval for TT₄ in clinically healthy rabbits.

TT₄ concentrations were determined by chemiluminescence assay (CLIA) in 120 clinically healthy pet rabbits (median age 36 months); the study population was divided into age groups (Group 1: 7-24 months, Group 2: 25-59 months, Group 3: > 60 months). The pet rabbits were kept indoors, outdoors, and indoor/outdoor. The reference interval (95 percentile) was calculated using SPSS (IBM, version 28.0) according to the standard of the ASVCP.

A median TT₄ concentration of 0.8 μg/dL (10.28 nmol/L) and a reference interval of 0.6-1.98 μg/dL (7.71-25.44 nmol/L) were determined. No statistically significant differences were found for sex (p = 0.889), age (p = 0.176), and between animals in indoor and outdoor housing (p = 0.967). Highly significant differences were observed between indoor and indoor/outdoor housing (p = 0.002) and significant differences between outdoor and indoor/outdoor housing (p = 0.006).

Concentrations of TT₄ in pet rabbits measured by chemiluminescence appear to be independent of sex and age. Laboratory and device-specific reference intervals for pet rabbits should be used to avoid the influence of different methods, devices, calculation methods, and sample size.