Handling procedures, types of tubes used, and time of year blood is drawn, all make a difference in the results
To diagnose Insulin Resistance, several tests are needed to get a complete picture of your horse’s condition. Equine Medical & Surgical Associates have consulted with numerous labs, companies supplying blood tubes, and universities (Harvard, John Hopkins, Stanford and the Mayo Clinic), and run hundreds of tests to see which tubes give the best results.
An Insulin Resistance test includes assessing levels of Insulin and Glucose; you should also test Thyroid levels and the ACTH.
Each test needs specific tubes, handled specific ways in the barn, during transport, and later in the lab to get accurate results. Poor handling in any of these steps will yield false information which can lead to your horse not getting the correct therapy.
What can the owner do to make testing more accurate?
1. Try to avoid conditions that would cause Insulin surges. Insulin and ACTH levels will go up if the horse is excited. The goal is to keep the routine and peace prior to blood testing. You, as the owner, know the best way to do that.
2. Tell the tester if the horse is sick. If Insulin/ACTH levels are sky high, it is probably stress and disease.
3. Tell the tester if the horse is on medications. Certain items like Bute and Banamine will lower thyroid blood levels causing false low results.
When to test?
To avoid seasonal hormonal surges of ACTH, do not test in the Fall. Wait until January or later.
Test insulin in the morning, approximately 2 hours after feeding some sweet feed. According to a 2008 study, Insulin peaks at 2-2.5 hours after feeding, even when feeding low carb/low starch diets. If you wait 3 hours, the Insulin drops 10% and you get a false low number. If you test in the afternoon, the number can be 40-50% lower than the peak. If you test in the afternoon, you may think your horse is OK, but actually it may be in trouble.
What to feed prior to the test?
Sweet Feed - If you feed little/no grain or a low carbohydrate grain, on testing day, feed a very small amount of sweet feed to see how your horse’s Insulin level reacts. This test means you will not have to have your horse tubed down with a dextrose sugar solution and have blood drawn 12 times – that is stressful and expensive. Our studies have found it only takes a very small amount of sweet feed to find true Insulin Resistance horses – for example about 2-3 handfuls to a pony. The goal is to find the horse's true Insulin status and a very small amount of grain will show this. Fasting or testing while the horse is eating only hay gives inferior information.
Hay/Fresh Grass – feed normal amount of hay you usually give in the morning. Turn out normally after you give the sweet feed, with a muzzle if that is routine, or without. We will test 2 hours later.
Why Sweet Feed?
1. Dr. Frank's 2006 AAEP article mentioned that fasting Insulin level tests will miss true Insulin cases at times. The fasting created a false low result.
2. Dr. Bailey's 2007 study showed that if only hay is fed to Insulin Resistance horses, their Insulin levels are the same as the normal control horses - again, a false negative. When these horses received a feed challenge, their Insulin tripled over the normal horses. Summary: Testing while only on hay will miss cases. For a horse to have a high Insulin while on just hay is not common.
3. It is only a soft challenge - Dr. Bailey's study gave much more sugar with NO HORSES GETTING LAMINITIS.
4. It is easy, inexpensive, and will pick up true Insulin Resistant horses needing help.
For specific testing procedures, including which tubes to use and when, click here .