Study reveals differing electrolyte measurements between point-of-care and reference analysers in dogs with hypoadrenocorticism

16 October 2020

A new study, published in the latest issue of the Journal of Small Animal Practice (JSAP), showed that there were inherent differences between the electrolyte concentrations measured by point-of-care analysers and reference laboratory methods in dogs with hypoadrenocorticism.

The study titled “Electrolyte measurements differ between point-of-care and reference analysers in dogs with hypoadrenocorticism” 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, as well as sodium-to-potassium ratios, in dogs diagnosed with and treated for hypoadrenocorticism.

Forty-eight dogs with hypoadrenocorticism were enrolled into a prospective cross-sectional study at the University of Glasgow. In total, 329 paired samples were measured on the Catalyst analyser and by the reference laboratory method called an ion selective electrode (ISE), while another 72 paired samples were tested on both the VetStat analyser and by ISE. The clinical effects of any difference in the electrolyte results were investigated.

Sam Fowlie, 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 relevance of the disagreement between these methods was investigated by assessing how often the point-of-care analysers produced results which fell outside their reference range when the ISE method found them to be within reference and vice versa. For the Catalyst, there were 21 cases (6%) with discordant sodium results, 27 cases (8%) with discordant potassium results and 46 cases (14%) with discordant chloride results. The VetStat, meanwhile produced results which disagreed with the ISE method in 19 cases (26%) for sodium, 3 cases (4%) for potassium measurement and 9 cases (13%) for chloride analysis.

Nicola Di Girolamo, Editor of JSAP added: “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.”

The full article can be found in the October issue of the Journal of Small Animal Practice and be read online here. The original early on-line version article has had some amendments pertaining to two minor flaws which do not affect the conclusions of the paper. It is open access and can be freely accessed by anyone.

The Journal of Small Animal Practice is published monthly and access to all articles is free for BSAVA members. For information on how to become a BSAVA member visit the website here.

1S. Fowlie, S. Spence, E. Roberts and I. K. Ramsey (2020) Electrolyte measurements differ between point-of-care and reference analysers in dogs with hypoadrenocorticism. Journal of Small Animal Practice, 61 (10). Available at: