Dogs receiving treatment for hypoadrenocorticism are typically monitored by analysis of their serum sodium (Na⁺) and potassium (K⁺) concentrations and the Na⁺:K⁺ ratio alongside their clinical signs. There is a desire for veterinarians to be able to measure these concentrations in-house, allowing same day dose changes as opposed to waiting for the results from a reference laboratory.

The aim of this study was to compare these electrolyte concentrations and Na⁺:K⁺ ratios obtained from two in-house electrolyte analysers (IDEXX Catalyst Dx® and IDEXX Vetstat®) with a reference laboratory (Olympus AU600) in a cohort of dogs with hypoadrenocorticism.

Cases (n=33) were prospectively enrolled into a clinical trial comparing fludrocortisone to DOCP in the treatment of hypoadrenocorticism. All dogs had multiple electrolyte measurements taken at various time points during treatment. A total of 343 samples were tested by the reference laboratory using the Olympus AU600 analyser. Of these, 280 samples were also tested using the Catalyst Dx® analyser and 61 by the Vetstat® analyser. Some samples were tested using all three analysers.

The Catalyst Dx® and Vetstat® showed good correlation to the Olympus AU600 for Na⁺ and K⁺ concentrations and Na⁺:K⁺ ratio. For the Catalyst Dx® these were r=0.714, 0.830 and 0.858, respectively, all with a p<0.0001. For the Vetstat® these were r=0.816, 0.955 and 0.959, all with a p<0.0001. The mean difference (Bland-Altman plot) for Na⁺ was -5.84 mmol/L with a standard deviation of 3.69 for the Catalyst Dx® and -11.67 mmol/L and 2.46 for the Vetstat®. The mean difference and standard deviation for K⁺ was -0.15 mmol/L and 0.36 respectively for the Catalyst Dx® and 0.01 mmol/L and 0.17 for the Vetstat®. Finally, the mean difference and standard deviation for the Na⁺:K⁺ ratio was -0.20 and 2.90, respectively, for the Catalyst Dx® and -3.07 and 1.83 for the Vetstat®.

Both in-house analysers displayed good correlation with the reference laboratory for the electrolytes measured. However, both analysers persistently recorded higher Na⁺ concentrations. Analysis of K⁺ concentrations was closer to the reference laboratory but the effect of the increased Na⁺ resulted in the Na⁺:K⁺ ratio also being higher. This could have clinically significant effects in the management of dogs with hypoadrenocorticism and care should be taken when using target ranges based on a reference analyser when using results from in-house electrolyte measurements.

Disclosures

Disclosures to report:

The lead author's position and this study are jointly funded by Dechra Ltd and the University of Glasgow.