Evaluation of Blood Biochemical Profiles in Hyperthyroid Cats of Different Age

Abstract

Hyperthyroidism is the most common endocrine disease of middle-aged and older cats, caused by excessive thyroid hormone production (1,2), but occurs in approximately 10% of older cats too, and is usually diagnosed when owners notice clinical signs (2,3). In cats with hyperthyroidism changes in serum biochemical parameters are often observed (4). After treatment, serum biochemical parameters change, and may help diagnose comorbidities (5). Therefore, it was important to monitor and analyse blood biochemical parameters in cats of different age with hyperthyroidism before and after treatment. For each of 55 cat with hyperthyroidism medical history was taken, and the diagnosis was confirmed by elevated TT4 levels (TT4 > 60 nmol/L) and the presence of clinical signs. The following blood biochemical parameters were assessed: ALT, ALP, CREA, UREA. Measurements were taken prior to treatment and again 3 to 6 weeks after thiamazole therapy, once euthyroidism was achieved (TT4 < 30 nmol/L). All cats were divided into three age groups: group I – under 11 years old, group II – aged 11 to 15 years, group III – over 15 years old. The most common clinical signs in hyperthyroid cats were weight loss (85.45 %), vomiting (50.91 %), and increased appetite (30.91 %). Higher CREA values were linked to weight loss and poor coat condition, while lower CREA values were associated with increased appetite (p < 0.05). Group II had the highest prevalence of hyperthyroidism (49.09 %). Blood UREA levels increased with age (p < 0.01), with older cats showing significantly higher levels. Elevated ALT levels were observed in most cats, exceeding the upper reference limit (p < 0.05). Posttreatment, ALT and ALP values decreased, while CREA and UREA concentrations increased (p < 0.001). The study highlights the importance of monitoring these parameters to diagnose and manage hyperthyroidism effectively, considering the biological characteristics of the cats.