The prevalence of hypocobalaminaemia in cats with spontaneous hyperthyroidism

Methods: Serum cobalamin concentrations were measured in 76 spontaneously hyperthyroid cats [serum thyroxine (T-4) concentration >= 100 nmol/L] and 100 geriatric euthyroid cats. Erythrocyte and neutrophil counts in hyperthyroid cats with hypocobalaminaemia were compared with those in hyperthyroid cats with adequate serum cobalamin concentrations (>= 290 ng/L). Results: The median cobalamin concentration in hyperthyroid cats was lower than the control group (409 versus 672 ng/L; P=0 center dot 0040). In addition, 40 center dot 8% of hyperthyroid cats had subnormal serum cobalamin concentrations compared with 25% of controls (P=0 center dot 0336). Weak negative correlation (coefficient: -0 center dot 3281) was demonstrated between serum cobalamin and T-4 concentrations in the hyperthyroid population, and the median cobalamin concentration was lower in cats with T-4 above the median of 153 nmol/L compared with cats with T-4 below this value (P=0 center dot 0281). Hypocobalaminaemia was not associated with neutropenia or anaemia in hyperthyroid cats. Clinical Significance: This study indicates that a substantial proportion of cats with T-4 >= 100 nmol/L are hypocobalaminaemic and suggests that hyperthyroidism directly or indirectly affects cobalamin uptake, excretion or utilisation in this species.