Cook A.K., Suchodolski J.S., Steiner J.M., et al.
OBJECTIVES: To determine the prevalence of hypocobalaminaemia in cats with moderate to severe hyperthyroidism and to investigate the relationship between cobalamin status and selected haematologic parameters. 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=0.0040). In addition, 40.8% of hyperthyroid cats had subnormal serum cobalamin concentrations compared with 25% of controls (P=0.0336). Weak negative correlation (coefficient: -0.3281) 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=0.0281). 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.