The aim of this study was to evaluate the association between serum methylmalonic acid (MMA), a proposed marker of cellular cobalamin deficiency, and serum cobalamin concentrations in dogs. Serum samples from 555 dogs were grouped according to their serum cobalamin concentrations (<150 ng/L to 1000 ng/L). Additionally, serum samples were collected from 43 healthy dogs to calculate a reference interval for canine serum MMA. MMA was measured using a GC/MS method. Groups were compared using a Kruskal-Wallis test with Dunn's post test. Proportions of dogs above the upper limit of the reference interval were calculated and a χ2-test for trend was performed to evaluate the association between serum cobalamin and MMA concentrations. The reference interval for serum MMA was calculated to be 414.7-1192.5 nmol/L. Dogs with serum cobalamin concentrations <251 ng/L had significantly higher MMA concentrations (P<0.05) and the χ2-test for trend showed a trend for increasing serum MMA concentrations with decreasing serum cobalamin concentrations (P<0.0001). Additionally, a number of dogs with normal serum cobalamin concentrations had increased serum MMA concentrations, suggesting that some of these dogs may have cobalamin deficiency on a cellular level. Further studies are warranted to determine if these dogs should receive cobalamin supplementation.
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