Dog’s treated for hypoadrenocorticism are routinely monitored through analysis of their blood electrolyte concentrations. This is often performed with point-of-care analysers to facilitate faster medication dose adjustments based on the results. The objective of this study was to investigate the performance of two point-of-care analysers (IDEXX Catalyst™ Dx and IDEXX VetStat®) against a reference laboratory indirect ion-selective-electrode method (Olympus AU640 or Siemens Dimenson Xpand Plus) for the measurement of blood sodium, potassium and chloride concentrations, as well as the sodium: potassium ratio, in dogs diagnosed with and treated for hypoadrenocorticism. Forty-eight dogs were enrolled into a prospective cross-sectional study. Paired blood samples were taken and tested on the two point-of-care analysers and at the reference laboratory. Statistical analysis was then performed with Spearman’s correlations, BlandAltman analysis, Passing-Bablok regression and Cohen’s Kappa analysis. The clinical effects of inaccurate electrolyte analysis were also considered. In total, 329 samples were tested on the IDEXX Catalyst™ Dx analyser, whilst another 72 samples were tested on the IDEXX VetStat®. Spearman’s correlations were acceptable for all electrolytes, but regression analysis identified both proportional and constant bias for some analytes. There was poor agreement between sodium and chloride concentrations on both analysers and they tended to give higher results than the reference ISE method for all analytes, except for potassium when measured on the IDEXX VetStat®. In conclusion, there are inherent differences between the electrolyte concentrations measured by these two point-of-care analysers and reference laboratory methods in dogs with hypoadrenocorticism. Clinicians should be aware of this and consistent in their method of measurement of electrolytes when monitoring these dogs.