Using corrected serum chloride and predicted bicarbonate concentrations to interpret acid-base status in dogs

Background Changes in water balance and the presence of unmeasured anions perturb the inverse relationship between serum chloride (Cl) and bicarbonate (HCO3) concentrations in people, affecting accurate interpretation of acid‐base status. Objectives The aim of this study was to demonstrate that corrected serum Cl and predicted HCO3 concentrations, based on serum sodium (Na) concentration and anion gap (AG), would be inversely correlated and could be used to better characterize causes of acid‐base disorders in dogs. Methods In this retrospective study, electrolyte data from dogs with at least one abnormality in serum Na, Cl, or HCO3 concentrations were analyzed. Profiles were classified before and after calculations using 2 methods, a modified Feldman and an institutional method, to correct Cl concentration and predict HCO3 concentrations based on Na concentration and AG. Dogs were classified as low (L), normal (N), or high (H) based on Cl (first letter) and HCO3 (second letter) concentrations, as follows: LL, LN, LH, NL, NN, NH, HL, HN, or HH. Results For profiles from 261 dogs, reclassifying corrected Cl and predicted HCO3 concentrations resulted in a shift from the initial classification into a different one in 73% of dogs; in most cases, the shift was to LH, NN, or HL categories. Albumin concentration was a significant factor in acid‐base balance. Conclusions When interpreting acid‐base status based on results of a standard biochemical panel, erroneous conclusions can be drawn if concentrations of Na, unmeasured anions, and albumin are not taken into account. The inverse relationship between serum Cl and HCO3 concentrations may be used to identify frequent acid‐base disorders as well as to unmask abnormalities obscured by irregularities in water balance or AG.