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Keywords:

  • acid-base status;
  • electrolytes;
  • homeostasis;
  • physiology

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.