Evaluation of Precision and Establishment of Reference Ranges for Plasma Thyroxine using a Point-of-Care Analyzer in Healthy Guinea Pigs (Cavia porcellus)

The objective of this study was to evaluate precision and establish a reference range in healthy guinea pigs for total plasma thyroxine (T4) using a point-of-care analyzer. One-hundred-nine (109) healthy pet and laboratory-housed guinea pigs were included in this study in which plasma T4 concentrations were measured on a point-of-care analyzer. Some of the samples were analyzed in duplicate and then compared using an intraclass correlation coefficient (ri) and coefficient of variance to assess precision. Statistical analysis was performed to test for normal distribution of data and a reference range was established. Differences in subsets of the tested population were evaluated using t tests and analysis of variance. The ri was 0.95 and the coefficient of variance was 4.2%. Data were normally distributed and a reference range for plasma T4 of 2.26 μg/dL to 5.82 μg/dL was established. No significant differences between or among mean plasma T4 concentrations were found when sexes, housing type, and sampling protocol were compared. In addition, no significant difference was found between the mean plasma T4 concentrations of 2 age groups (2 months and 8 months). The overall precision of this testing modality was determined to be excellent, indicating that measuring plasma T4 with enzyme immunoassay on the point-of-care analyzer yields consistently repeatable results. This study successfully defined plasma T4 reference intervals specific to a point-of-care analyzer in normal guinea pigs. Our results showed that age (2 months and 8 months), sex, housing type, and sampling protocol have no significant effect on the mean plasma T4, although pet-housed guinea pigs had a wider reference interval than laboratory-housed guinea pigs.