Serum myoglobin, creatine kinase, and cell‐free DNA in endurance sled dogs and sled dogs with clinical rhabdomyolysis

OBJECTIVE: To evaluate whether cell-free DNA (cfDNA) concentrations are increased in dogs with exertional rhabdomyolysis and whether concentrations are correlated with serum myoglobin concentration and creatine kinase activity. DESIGN: Observational cohort study. SETTING: Yukon Quest 1,000-mile International Sled Dog Race 2015. ANIMALS: Twelve normal competitive sled dogs; 5 dogs with rhabdomyolysis. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Blood was collected from all confirmed cases of exertional rhabdomyolysis and compared to the winning team at the midrace point. Results indicate that median cfDNA did not increase, but decreased by the race finish (prerace = 314.2 ng/mL versus midrace = 283.7 ng/mL versus postrace = 249.5 ng/mL). There were no rises in median cfDNA in dogs with rhabdomyolysis (255 ng/mL) negating its potential utility as a measure of acute skeletal muscle compromise. In contrast, myoglobin concentration and creatine kinase activity at the midrace point for normal dogs were significantly lower than dogs with rhabdomyolysis. Values for myoglobin and creatine kinase were strongly positively correlated (R = 0.91). CONCLUSIONS: cfDNA is not a useful biomarker for exertional rhabdomyolysis in contrast to myoglobin and creatine kinase. Further evaluation of timing and clinical signs suggests that exertional rhabdomyolysis occurs early in endurance activities. Among the dogs with rhabdomyolysis, the dog that demonstrated clinical signs had the highest serum creatine kinase activity and myoglobin concentration.