Determination of strong ion gap in healthy dogs

Abstract

Objective: To determine and compare reference intervals of the strong ion gap (SIG) in a group of healthy dogs determined with 2 different equations. Design: Prospective observational study. Setting: Tertiary referral and teaching hospital. Animals: Fifty-four healthy dogs. Interventions: None. Measurements: Serum biochemistry and blood gas analyses were performed for each dog. From these values, SIG was calculated using 2 different equations: SIG1 = SIDa{[Na +] + [K+] - [Cl-]+ [2 × Ca2+] + [2 × Mg2+] - [l-lactate]}- SIDe {TCO2 + A-} and SIG2 = [albumin] × 4.9-anion gap. Reference intervals were established for each SIG equation using the mean ± 1.96 × standard deviation (SD). Results: For SIG1, the median was 7.13 mEq/L (range, 1.05-11.30 mEq/L) and the derived reference interval was 1.85-10.61 mEq/L. Median SIG2 was -0.22 mEq/L (range, -5.34-6.61 mEq/L) and the mean SIG2 was -0.09 mEq/L (95% confidence interval for the mean, -0.82-0.65 mEq/L). The derived reference interval was -5.36-5.18 mEq/L. The results of the SIG calculations were significantly different (P < 0.0001) between the 2 equations used. Conclusion: The 2 equations used to calculate SIG yielded significantly different results and cannot be used interchangeably. The authors believe SIG2 to be a more accurate reflection of acid-base status in healthy dogs, and recommend that this calculation be used for future studies. © Veterinary Emergency and Critical Care Society 2012.