The relationship of serum cobalamin to methylmalonic acid concentrations and clinical variables in cats.
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BACKGROUND: Serum cobalamin concentration [CBL] suggests CBL deficiency in cats but serum methylmalonic acid concentration [MMA] more accurately indicates CBL deficiency. OBJECTIVE: To examine the ability of [CBL] to predict CBL deficiency defined by increased [MMA], and relationships of [CBL] and [MMA] with select clinical and clinicopathological variables. ANIMALS: One hundred sixty-three client-owned cats with [CBL] measurements, 114 cats with simultaneous [MMA] measurements; 88 cats with medical information. METHODS: Prospectively collected [CBL] and [MMA] were compared using scatter plots, receiver operating characteristic and correlative analyses with historical [CBL] thresholds and those identified in the study. [CBL] and [MMA] were compared retrospectively to specific clinical and clinicopathological variables. RESULTS: [CBL] correlated negatively with [MMA] ( = -0.334, P < .0001). [MMA] 1,343 nmol/L identified CBL deficiency. [CBL] = 209 pg/mL optimized sensitivity (0.51), specificity (0.96), PPV (0.89), and NPV (0.74) for detecting [MMA] 1,343 nmol/L. Prevalence of CBL deficiency was 42% (48/114) when defined by [MMA] 1,343 nmol/L versus 23% (27/114) by [CBL] 209 pg/mL. Unexpectedly, 23 and 45% of 48 cats with [MMA] 1,343 nmol/L had [CBL] > 900 pg/mL and 290 pg/mL (historical thresholds). [CBL] correlated with mean corpuscular volume ( = -0.199, P = .013) and [MMA] with hematocrit ( = -0.28, P = .006). CONCLUSIONS AND CLINICAL IMPORTANCE: Cobalamin deficiency ([MMA] 1,343 nmol/L) occurred in 42% of cats and is predicted with high specificity by [CBL] 209 pg/mL. CBL status correlates with microcytosis and anemia. Discordance between [CBL] and [MMA] cautions against relying on any single marker for determining CBL status.
