Determination of a plasma retinol reference interval in eastern collared lizards (Crotaphytus collaris)

Background

The Eastern collared lizard (Crotaphytus collaris) is a species of lizard native to the United States and Mexico and is growing in popularity in the exotic community around the world. There is minimal knowledge known on the analyte breakdown of this or closely related species. As this species becomes more popular in the exotic community more medical conditions are being identified that can be assisted in diagnosis with the establishment of ranges of the different essential analytes. Being an insectivorous lizard, this species may suffer from hypovitaminosis A. There has been a lack of antemortem diagnostics available for minimally invasive and appropriate diagnosis of this disease. Recent studies have been performed in other small insectivore species establishing plasma retinol reference intervals. Reference intervals for retinol have not been published or validated in collared lizards or any closely related species.

Methods

Plasma, with a sample volume of only 50 µl, from forty clinically healthy captive bred Eastern collared lizards, twenty males and twenty females were analyzed using ultra-high-performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS) to determine plasma retinol concentrations.

Results

Using UPLC-MS/MS analysis, data was normally distributed and a reference interval for plasma retinol in the Eastern collared lizard was 1.57-3.07 µg/mL (0.237-0.464 µmol/L). A mean of 0.31µg/mL; with a lower limit 95% confidence interval being 1.34-1.80 µg/mL and upper limit of 2.84-3.30 µg/mL. Vitamin A (retinol) levels were significantly different when comparing a captive bred line called Blazing Blue (n = 4), with all other sampled captive bred localities. Including a closely related Aquaflames (n = 16), (Sky Blue) (n = 2), Western yellowhead (n = 5), Fancy Spotted (n = 4), Aquamarine (n = 3), and Lightning Yellow (n = 6); with the Blazing Blue morph being significantly lower using a t-Test comparison assuming equal variations. There was only 1 statistical variation seen in age groups between the 1-year-old and 6-year-old age groups with the 6-year-old age group being significantly lower than the 1-year-old age group. There was no variation based on sex.

Conclusions and clinical relevance

This study provides the first established plasma retinol range in a species in the suborder iguania. Values are valuable in assistance in diagnosing and treating hypovitaminosis A and to provide advice on dietary supplementation and dietary improvement for the collared lizards and possibly other related species as well. In addition, these values can be used to design and evaluate other studies for nutritional needs of this species. Limitations of this study include only a single season of collection, no same time comparison to liver values, some age groups were limited to only 1 individual, and the evaluation of only captive bred individuals.