A comparison of thyroid hormone levels and plasma capillary zone electrophoresis in red-eared sliders (Trachemys scripta elegans) and map turtles (Graptemys spp.) depending on season and sex
Thyroid hormones and capillary zone electrophoresis are rarely studied in reptile medicine. The goal of this prospective study was to establish RIs for plasma proteins and thyroid hormones, total tetraiodothyronine (tT4), free T4 (fT4), total triiodothyronine (tT3), and free T3 (fT3), as well as iodine blood levels in red-eared sliders (Trachemys scripta elegans) and map turtles (Graptemys spp.). Variables were measured over 1 ½ years to determine variations depending on sex and season, as well as any correlations between the parameters. A total of 131 blood samples from red-eared sliders and 51 blood samples from map turtles were collected from May 2016 to November 2017. The levels of tT4, fT4, and fT3 were measured using standardized autoanalyzer test systems; tT3 was measured by ELISA and iodine inductively coupled plasma mass spectrometry. Total protein was quantitated using the biuret method, and plasma protein fractions were measured using capillary zone electrophoresis. The results showed significant variations in thyroid hormone levels and plasma protein fractions depending on sex and season. Total T4 and fT4 concentrations were significantly (P < .05) correlated in both turtle species and sexes in all seasons. Thyroid hormone levels correlated with blood proteins in a few seasons, including a positive correlation between tT4 and fT4 in female red-eared sliders in fall and female map turtles in summer and fall. This study demonstrates the importance of considering species, season, and sex variations when interpreting thyroid hormone and plasma protein levels. It also shows that thyroid hormone levels are not always influenced by total protein and albumin.