Agreement of 2 electrolyte analyzers for identifying electrolyte and acid-base disorders in sick horses.
Authors: Gomez Diego E, Buczinski Sébastien, Darby Shannon, Palmisano Megan, Beatty Sarah S K, Mackay Robert J
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: Electrolyte Analyser Agreement in Equine Acid-Base Assessment When managing critically ill horses, clinicians often rely on blood gas analysers to measure electrolytes and interpret acid-base status using the strong ion difference (SID) model; however, this retrospective study of 124 hospitalised horses reveals that different analyser platforms can produce substantially different results, with significant implications for diagnosis. Researchers compared paired samples from the same horses analysed on a Beckman Coulter chemistry analyser and a Nova Biomedical point-of-care device, examining both raw electrolyte values and derived SID parameters (SID4 and unmeasured strong ions). Although sodium and chloride showed reasonable agreement (mean bias of -1.2 and +4.4 mmol/L respectively), the calculated SID4 and USI variables demonstrated poor concordance, with intraclass correlation coefficients of just 0.55 and 0.2 respectively, meaning the two devices agreed on abnormalities only 20% of the time for SID4 and essentially not at all for USI. These methodological differences are not merely academic: depending on which analyser your practice uses, the same horse could be classified as having entirely different acid-base disorders, potentially leading to misguided therapeutic decisions. Practitioners using the SID approach should be aware that switching between analyser platforms may necessitate reinterpretation of results, and establishing which device your practice uses—and preferably maintaining consistency—is important for reliable longitudinal assessment of acid-base balance in hospitalised cases.
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Practical Takeaways
- •When using strong ion difference analysis for acid-base assessment in sick horses, be aware that different laboratory analyzers may produce different results and potentially different clinical interpretations—consistency in which analyzer is used for an individual case is important
- •The simplified SID approach may not be reliable for diagnosis when measurements come from different analyzer platforms; consider using traditional acid-base parameters (pH, pCO2, HCO3-) as a more standardized alternative
- •If serial electrolyte and acid-base monitoring is needed in hospitalized horses, ensure samples are analyzed on the same machine throughout the case to maintain consistency in interpretation
Key Findings
- •Mean bias for Na+ was -1.2 mmol/L, Cl- was 4.4 mmol/L, SID4 was -5.4 mmol/L, and USI was -6.2 mmol/L between the two analyzers
- •Intraclass correlation coefficient for SID4 was 0.55 and for USI was 0.2, indicating poor to moderate agreement
- •Poor agreement between analyzers for detecting SID4 abnormalities (κ = 0.20) and USI abnormalities (κ = -0.04)
- •Methodologic differences in analyzer technology led to discordant acid-base disorder diagnosis using the simplified strong ion difference approach