Effect of age on anion gap in clinically normal Quarter Horses

Anion gap [AG = (Na + K) - (Cl + HCO3)] was determined in Quarter Horses: 10 clinically normal foals 0.5 to 3 days, 2 to 3 weeks, and 5 to 7 weeks of age; 10 yearlings; and ten 2-year-olds. Mean AG (+/- 1 SD) were 12.8 +/- 3.3, 15.2 +/- 2.9, 14.0 +/- 1.6, 12.3 +/- 1.8, and 10.4 +/- 1.2 mEq/L, respectively. The 4 to 5 mEq/L higher AG in 2- to 7-week-old foals, when compared with that in 2-year-old horses, can be explained in part by hyperphosphatemia (2 mEq/L) and lower calcium values (0.4 mEq/L). Decreased globulin concentrations may also contribute to the higher AG. The AG can be useful in the diagnosis and prognosis of metabolic imbalances in the horse. The age of the animal was important in the interpretation of AG. Age adjustment of reference intervals will increase the usefulness of AG in foals.