Prospective evaluation of clinical, laboratory and scintigraphic features of naturally occurring hypothyroidism in 4 adult cats

Methods Submissions (geriatric profile, total thyroxine [TT4]) to a commercial laboratory between January 2022 and April 2023 were prospectively screened for cats with low TT4 aged 3-12 years. In these cats, TSH was measured. Iatrogenic hypothyroidism due to hyperthyroidism treatment was excluded by contacting submitting veterinarians. Creatinine and cholesterol concentration and red blood cell count (RBC) of cats with suspected spontaneous hypothyroidism (low TT4, TSH > 0.53 ng/ml [total allowable error of the upper reference range (RR)]) was compared to cats with TT4 within RR and cats with low TT4 but normal TSH (< 0.3 ng/ml; laboratory upper RR) by non-parametric tests. Data is presented as medians. Significant was P<0.05. Cats with suspected hypothyroidism were invited for thyroid scintigraphy and TSH stimulation test.