Emily Clark, Ian Ramsey

Small Animal Hospital, School of Biodiversity, One Health and Veterinary Medicine, University of Glasgow, Glasgow, United Kingdom

Objectives

To investigate whether serum TSH measurement helps predict the development of azotaemia in cats following I-131 administration.

Methods

Single-centre retrospective observational study involving hyperthyroid cats that were treated with I-131. T4 and creatinine concentrations were measured before I-131, at 2-4 weeks post-treatment, and 2-4 months post-treatment. TSH concentration was measured at 2-4 months post-treatment. Cats were categorised based on their thyroid status at 2-4 months: euthyroid (T4 15-50nmol/L) with normal TSH concentrations (≤ 0.3ng/ml) (EU), hypothyroid with normal TSH concentrations (NTSH), or hypothyroid with high TSH concentrations (HTSH). The mean creatinine values at 2-4 months were compared between the groups.

Results

Forty-five cats were included in the study (EU = 20; NTSH, n = 13; HTSH, n = 12). The mean creatinine concentrations of the EU, NTSH, and HTSH groups were significantly different (125.5umol/L, 148.6umol/L, and 176.7umol/l respectively). The proportions of cats in each group with azotaemia (creatinine >180umol/l) were also significantly different. There were significant differences between the mean ages but not the median I-131 doses between the groups, with the HTSH group being significantly but only slightly older.

Statement: Impact/ Clinical Significance

These results support measuring serum TSH in cats with a low T4 2-4 months after I-131 treatment as an indicator of risk of azotaemia. It is likely that those cats that have a low T4 but a normal TSH are less likely to develop azotaemia in the future and may not therefore require T4 supplementation.