Insulin Resistance: Variation in Blood Test Levels

A blood sample is usually a key step in diagnosing a horse as insulin resistant. But a recent study showed that one sample might not give enough information for an accurate diagnosis, because the horse's blood sugar and insulin fluctuates daily.

"Your veterinarian should probably take at least two samples on different days," recommended Shannon E. Pratt, PhD, of North Carolina State University, who recently completed a study on the topic.

For six days, Pratt and her colleagues took blood samples from six horses that had not been fed for four hours. The researchers measured the insulin and glucose concentrations, finding "significant day-to-day variation, which means that the results from a single blood sample aren�t entirely reliable," Pratt said.

Insulin resistance has been associated with an increased risk of laminitis and metabolic syndrome. If an owner wants to help the veterinarian get the best blood samples for testing, Pratt suggested that animals should not be fed nor exercised for at least four hours before the test.

"This will minimize fluctuations in glucose and/or insulin that would be due to the meal," she said.

If the insulin measurements are between 20-30�/ml, the horse should probably be monitored and retested in the future. If the horse�s insulin values are above 30 �/ml, then the horse might be insulin resistant.

If the horse is insulin resistant, owners might consider measuring glucose regularly to make sure that dietary or other interventions are working to keep blood sugar from fluctuating too much. Pratt said that just because a horse is fat, it won't necessarily develop insulin resistance, but carrying extra pounds does increase the risk.

The study, "Variation of insulin sensitivity estimates in horses," was published in the July 2009 Journal of Equine Veterinary Science. The abstract is available online.  

About the Author

Marie Rosenthal, MS

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