Assessment of the use of plasma and serum chloride concentrations as indirect predictors of serum bromide concentrations in dogs with idiopathic epilepsy.

Background: Bromide (BR) administration causes pseudohyperchloremia when plasma or serum chloride (Cl-) concentrations are determined with commonly available automated analytical assays. In humans receiving BR, it has been previously demonstrated that the plasma Cl- concentration is a useful indirect estimator of the measured BR concentration.

Objective: The objective of this study was to determine if the magnitude of pseudohyperchloremia seen in epileptic dogs treated with BR could be used as a predictor of the measured serum BR concentration.

Methods: Plasma and serum Cl- concentrations, analyzed by ion-specific electrode (ISE) and colorimetric techniques, and serum BR concentrations, determined using the gold-trichloride assay, were simultaneously determined in 88 blood samples from dogs with idiopathic epilepsy that were treated with BR.

Results: For all methods used to quantify Cl- concentrations, there were significant (P < .0001) linear relationships between BR and Cl- concentrations. Linear relationships between BR and Cl- concentrations were significantly different (P < .0001) between blood samples from dogs obtained during routine therapeutic monitoring and those obtained during emergency hospital admissions. Calculated 95% prediction intervals for future values of BR using measured Cl- concentrations contained considerable error. Plasma Cl- values determined with ISE generally provided the best prediction of serum BR concentrations. Agreement between the measured BR and Cl- using all Cl- assay techniques was moderate, but was statistically significant only when Cl- was assayed in plasma using one ISE method.

Conclusions: The pseudohyperchloremia observed in epileptic dogs receiving BR is an inadequate indirect estimator for the measured BR concentration, although in certain clinical situations identified through construction of a clinical decision tree, the measured Cl- value can be used to guide general therapeutic decisions regarding alterations in BR therapy. Optimal tailoring of BR therapy in dogs with idiopathic epilepsy should be based on results of therapeutic monitoring of BR concentrations.