Serum fructosamine concentrations in hyperthyroid cats

Serum fructosamine concentrations were measured in 35 healthy cats and in 3 0 hyperthyroid cats before and 30 days after curative radioiodine (I-131) t reatment. Hyperthyroid cats were divided into those with 30 day post-treatm ent total thyroxine (T4) concentrations within (EuT4) or below (HypoTL) the reference range. The median (semi-interquartile range, SIR) fructosamine c oncentration was significantly lower in hyperthyroid compared with healthy cats (295.0 (18.5) mu mol l(-1)) both before (254.0 (27.6) mu mol l(-1)) an d after (268.5 (28.0) mu mol l(-1)) treatment (P < 0.001 in each case). I-1 31 therapy was associated with increases in serum fructosamine (mean increa se 20.4 mu mol l(-1), P = 0.039) and total protein (6.3 g l(-1), P < 0.002) in the HypoT4 group and in globulin concentration in both EuT4 (5.9 g l(-) , P < 0.002) and HypoT4 (5.2 g l(-1), P = 0.023) groups. There were no dire ct relationships between the observed elevations in fructosamine concentrat ion and those in total protein or globulin concentrations suggesting that t he effect may be due to reduced rates of protein turnover. Reduced values m ay need to be considered when interpreting serum fructosamine concentration s for monitoring the degree of glycaemic control in diabetic cats with conc urrent hyperthyroidism. (C) 1999 Harcourt Publishers Limited.