Agreement of 2 electrolyte analyzers for identifying electrolyte and acid‐base disorders in sick horses

Background Use of different analyzers to measure electrolytes in the same horse can lead to different interpretation of acid‐base balance when using the simplified strong ion difference (sSID) approach. Objective Investigate the level of agreement between 2 analyzers in determining electrolytes concentrations, sSID variables, and acid‐base disorders in sick horses. Animals One hundred twenty‐four hospitalized horses. Methods Retrospective study using paired samples. Electrolytes were measured using a Beckman Coulter AU480 Chemistry analyzer (PBMA) and a Nova Biomedical Stat Profile (WBGA), respectively. Calculated sSID variables included strong ion difference, SID4; unmeasured strong ions, USI; and total nonvolatile buffer ion concentration in plasma (Atot). Agreement between analyzers was explored using Passing‐Bablok regression and Bland‐Altman analysis. Kappa (κ) test evaluated the level of agreement between analyzers in detecting acid‐base disorders. Results Methodologic differences were identified in measured Na+ and Cl− and calculated values of SID4 and USI. Mean bias (95% limits of agreement) for Na+, Cl−, SID4, and USI were: −1.2 mmol/L (−9.2 to 6.8), 4.4 mmol/L (−4.4 to 13), −5.4 mmol/L (−13 to 2), and −6.2 mmol/L (−14 to 1.7), respectively. The intraclass correlation coefficient for SID4 and USI was .55 (95%CI: −0.2 to 0.8) and .2 (95%CI: −0.15 to 0.48), respectively. There was a poor agreement between analyzers for detection of SID4 (κ = 0.20, 95%CI, 0.1 to 0.31) or USI abnormalities (κ = −0.04, 95%CI, −0.11 to 0.02). Conclusions and Clinical Importance Differences between analyzer methodology in measuring electrolytes led to a poor agreement between the diagnosis of acid‐base disorders in sick horses when using the sSID approach.