A formulation for stabilizing enzymatic activity and immunoreactivity of creatine kinase and creatine kinase isoenzymes comprising animal serum, creatine kinase and/or creatine kinase isoenzymes, an effective amount of a buffer having a pKa in the range of 6.2-7.6 to maintain pH of the formulation at 6.7+/-0.1, an effective amount of a non-thiol antioxidant to prevent oxidation of creatine kinase or creatine kinase isoenzyme thiol groups, an effective amount of a non-reducing polyol to stabilize immunoreactivity of creatine kinase or creatine kinase isoenzymes, and an effective amount of an antimicrobial to prevent microbial growth is provided.
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