Non-radiometric immunoassays [fluoroimmunoassay (FIA) and fluorometric enzyme immunoassay (FEIA) with radioimmunoassay (RIA) for evaluation of adrenal function in normal and hypercortisolemic dogs

RESUMO

Non-radiometric immunoassays offer many advantages over radiometric assays, such as higher stability of kit compounds and absence of potential hazardous effects for users and environment. The comparison of cortisol measurements by fluoroimmunoassay (FIA) and fluorometric enzyme immunoassay (FEIA) with radioimmunoassay (RIA) in adrenal function evaluation of normal (n=50) and hypercortisolemic dogs (n=12) was proposed. Serum concentrations of cortisol were measured in basal conditions and 8 hours after dexamethasone (DEX) suppression (0.01mg/kg/IV). All our reference values were based on the 5th and 95th percentile. The values for basal cortisol of healthy dogs were 0.20 to 2.35mg/d for FIA, 0.30 to 5.39mg/d for FEIA, and 0.65 to 4.64mg/d for RIA. After DEX suppression the values were <0.87mg/d, <0.30mg/d and < 0.80mg/d for FIA, FEIA and RIA, respectively. In hypercortisolemic dogs, the values of cortisol (mean ± SD) in basal and post-DEX conditions were 2.71 + 0.41mg/d and 1.73 + 1.15mg/d for FIA, 7.05 + 2.85mg/d and 4.93 + 2.26mg/d for FEIA, and 4.80 + 1.43mg/d and 3.52 + 1.08mg/d for RIA. Statistically significant differences (p<0.05) between the normal and the hypercortisolemic groups (Kruskal-Wallis test) were observed in the three methods, and between basal and post-DEX values (Wilcoxon test) using RIA and FEIA methods but not with FIA. Cortisol determinations by FEIA and RIA methods at DEX suppression test showed 100% of sensitivity and specificity for the diagnosis of hyperadrenocorticism in dogs. The results demonstrate that serum cortisol concentrations measurements by FEIA is a suitable alternative to the traditional RIA method for adrenal function evaluation in dogs.