SAIM Resident CSU VTH Fort Collins, CO, United States
Abstract: Background - Thyroid stimulating hormone (TSH) is currently measured in cats in some laboratories using a chemiluminescent immunoassay (CLIA) optimized for canines (Immulite 2000; Siemens). An in clinic assay using acoustic wave technology (Truforma® TSH-BAW; Zomedica) for use with feline sera is now available. Hypothesis/Objectives - To evaluate the stability of TSH in serum following long-term storage and to compare feline TSH concentrations determined by the CLIA and TSH-BAW assays. Animals - Stored (-80°C) sera from hyperthyroid cats (n = 13) before (week 0) and after (week 4) treatment with I-131. Methods- The 26 samples were stored for up to 24 months prior to this study. The week 0 samples had all been assayed by CLIA during the initial workup. Pre- and post-storage CLIA results and CLIA and TSH-BAW results before and after I131 treatment were compared. Results - Of the 7 samples initially positive by CLIA, 6 were positive after storage. One sample that was originally below the cutoff (< 0.03 ng/ml) was positive after storage (0.033 ng/ml). Of the 26 samples before and after I131, 8 were positive by TSH-BAW and 7 were positive by CLIA; all but 1 positive were post-treatment samples. The one discordant sample was post I131 and had values of < 0.030 ng/ml by CLIA and 0.028 ng/ml by TSH-BAW. Conclusions and clinical importance- Feline TSH appears to change minimally when stored frozen. In some situations, results of the TSH-BAW may classify the status of a cat with thyroid illness more accurately than the CLIA.
