"Clinicians should always use method-specific thresholds and, if these are not available, then they should exercise greater caution in their interpretation.”

Researchers identify differences in electrolyte measurements between point-of-care and reference analysers.

Researchers at the University of Glasgow have revealed inherent differences between the electrolyte concentrations measured by point-of-care analysers and reference laboratory methods in dogs with hypoadrenocorticism.

Canine hypoadrenocorticism - also known as Addison's disease - is a rare, life-threatening condition caused when adrenal glands fail to produce enough hormones for normal body function.

The study, published in the Journal of Small Animal Practice, investigated the performance of two point-of-care analysers (IDEXX Catalyst Dx and IDEXX VetStat) against a reference laboratory method for the measurement of blood sodium, potassium and chloride concentrations. It also looked at sodium-to-potassium ratios in dogs diagnosed with hypoadrenocorticism.

Some 48 dogs with hypoadrenocorticism were enrolled in the study, in which a total of 329 paired samples were measured on the Catalyst analyser and by the ion-selective electrode (ISE). Researchers tested another 72 paired samples on both the VetStat analyser and by ISE.

Sam Fowlie, a corresponding author for the paper, said: “Our results indicate that the sodium, potassium and therefore the sodium-to-potassium ratios, as well as the chloride concentrations measured by the Catalyst and VetStat analysers, may not be used interchangeably with those from a reference laboratory analyser using an indirect ISE method.

"Both analysers tended to give higher results than the reference method for all analytes, except for potassium when measured on the VetStat.”

The clinical effects of any difference in the electrolyte results were also investigated. For the Catalyst, there were 21 cases with discordant sodium results, 27 cases with discordant potassium results and 46 cases with discordant chloride results. The VetStat meanwhile produced results which disagreed with the ISE method in 19 cases for sodium, three cases for potassium measurement and nine cases for chloride analysis.

JSAP editor Nicola Di Girolamo, said: “This study reveals significant systematic differences (“bias”) between the three analysers in this study. Comparing numerical results from different analytical methods – be they point-of-care or reference laboratories – can be dangerous for patients.

"Clinicians should always use method-specific thresholds and, if these are not available (for example the sodium-to-potassium ratios on some analysers), then they should exercise greater caution in their interpretation.”

Image (C) Ian Ramsey.