Creatine kinase reference intervals at rest and after maximal exercise in Standardbred racehorses

Due to the high variability of data drawn from the literature, the aim of this study was to evaluate the effects of exercise on serum creatine kinase (CK) activity and to determine CK reference intervals (RIs) at rest and post-exercise in Standardbred racehorses. Data concerning history, physical examination, laboratory evaluation and ECG were collected retrospectively from a population of 258 Standardbreds in training that underwent incremental maximal treadmill exercise. Subjects with alterations potentially influencing CK were excluded. A reference sample of 194 healthy horses was eventually selected. Blood samples were collected 1 h before and 6 h post-exercise and analysed via a spectrophotometric method. Values were compared by Wilcoxon test for paired samples. The effect of age and sex was evaluated by Kruskal-Wallis and Dunn’s post-test (P<0.05). RIs were determined following Clinical and Laboratory Standard Institute (CLSI) guidelines, approved by the American Society for Veterinary Clinical Pathology. Using a macroinstruction set for Microsoft Excel (RefValAdv), RIs were determined with a non-parametric method. A significant increase (P<0.0001) in CK activity post-exercise was observed. Partition by sex and age did not show any statistical difference, either at rest or post-exercise. In determination of RIs no outliers were identified. RIs ranged from 25-394 IU/l at rest and from 44-734 IU/l post-exercise. To our knowledge, this is the first study considering CK post-exercise RIs in racehorses using CLSI’s guidelines and specific CK-related exclusion criteria. These RIs could be useful to discriminate between physiological and pathological post-exercise serum CK increases.