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Equine Health Resource

Blood Insulin & Glucose Levels



This test is performed as part of a diagnostic work up for horses suspected of having insulin resistance. Insulin is the hormone responsible for the regulation of blood sugar (glucose) levels. An insulin resistant horse is expected to have high insulin levels and high blood sugar levels.

Horses are fasted for at least 8 hours prior to blood sampling. It is important that they not be fed high sugar feeds in the hours prior to testing. Blood is sampled and submitted to a reference laboratory. Insulin levels above a normal range in the face of high or normal glucose indicates insulin resistance. A horse with excessive insulin and very low blood sugar could have an insulin producing tumor.


This is a relatively simple and cost-effective test for the diagnosis of insulin resistance, a very common problem for domestic horses. It only requires one sample of blood.


If horses do not fast prior to the test, the results could be erroneous. Glucose tolerance testing provides more information than this single sample test provides. Complete fasting causes stress, which elevates the stress hormone cortisol which in turn elevates glucose. Therefore one flake of grass hay 8-10 hours prior to testing is recommended.

Author: Doug Thal DVM Dipl. ABVP


Lavoie JP, Hinchcliff KW eds. Blackwell's 5 Minute Vet Consult: Equine. 2nd Ed. Ames: Wiley Blackwell 2008.Pers Comm. Ron Vin, Idexx Labs: March 2013.


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