Why A Muscle Enzyme Test is Important for Race Horses

Standardbred trainers will routinely have veterinarians pull blood on their horses in order to monitor blood counts, and other chemical levels within an equine athletes' system. Muscle enzyme levels are a part of this simple blood test/chemistry profile, and are used to help veterinarians with their diagnosis and treatment of a patient.

Typically, there are two muscle enzymes whose levels can be read by a testing laboratory: aspartate aminotransferase (AST-also known as SGOT or GOT) and creatine kinase (CK).

Because of the differences in labs, the machines used in the testing and the people who operate the machines, levels vary slightly from lab to lab, although the reference ranges will generally be provided along with the results of the test.

Veterinarians who study a horse's AST and CK levels, are in most cases, trying to find out if a horse has suffered from tying-up, or in technical terms, Equine Rhabdomyolysis Syndrome.

AST and CK levels are very close, and the rate at which they rise and fall is usually dramatically different, and this is how veterinarians diagnose how critical the situation is for the horse.

The scenario works like this: the veterinarian will pull a vial of blood from the horse and send it out to a laboratory. The lab tests the blood and the results are presented to the trainer the following day.

The results will show the chemistry that was tested (i.e., usually 15 or more separate entities, including: red and white blood counts, AST, CK, Glucose, Phosphorous, etc.), the results and the units (amounts), the reference ranges (giving the highs and lows of where the levels should fall), and any remarks about the test (if the range was higher or lower than normal levels).

The typical range for the AST levels are from 500 and lower, while CK levels can vary from 200 to 500. These are basic parameters that veterinarians use to monitor a horse's system. By monitoring the times of elevation of the AST and CK levels, veterinarians can determine if the case of typing-up is in the early or late stages of the syndrome.

When tying-up, a horse's AST levels peak after about eight hours and have a half-life of seven to eight days, while in contrast CK levels peak within two to six hours and have a half-life of around two hours. These differences are what veterinarians use to help evaluate the stage of muscular damage and thus, treatment.

If the condition is in the acute stage, treatment is more aggressive. The horse may show outward signs of stiffness and can be quite uncomfortable. Vets will usually recommend immediate treatment of anti-inflammatories, such as banamine and a muscle relaxant such as robaxin. Electrolyte fluids are also often given at this stage.

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