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How to Test for Insulin Resistance:

A.    To diagnose Insulin Resistance, your doctor will need to test several items in order to get a complete picture of your horse’s condition.  This is a key point in the HEIRO™ Laminitis prevention program.  Another key point is that most doctors and labs are unaware of special handling procedures in testing for Insulin Resistance.  We have consulted with numerous labs, supply companies of blood tubes, and universities such as Harvard, John Hopkins, Stanford and the Mayo Clinic.  We have run hundreds of tests to see which tubes give the best results and we enthusiastically share this information with owners in order to help their horses.

The two main items of Insulin Resistance to test for are Insulin and Glucose, but also test the Thyroid levels and the ACTH.

 * If you suspect Cushings, run Insulin Resistance tests.  If you suspect Insulin Resistance, run Cushings blood tests.

 Each test needs specific tubes, handled specific ways both in the barn, and later, in the lab or car in order 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.

B.   What can I do as the owner to make testing more accurate?

1.   The goal is to keep the routine and peace prior to blood testing.  You, as the owner, know the best

Extended pain from any condition will cause Insulin surges

way to do that.  Insulin and ACTH levels will go up if the horse is excited — if it is a rodeo to catch the horse, we will get a false elevation.  If you usually turn out after grain, and they are easy to catch/sweethearts in the field, then pull blood in the field.  If the horse is tough to catch in the field, keep them in with other horses.  Provide hay as you usually do after giving grain.  If you turn out, put a muzzle on if you usually do, or if you do not, and then just turn out.
2.   Tell the doctor if the horse is sick.  Besides excitement, sickness, high stress of recent show/shipping or current laminitis is enough stress to elevate Insulin/ACTH which makes testing difficult.  If we test these horses and get high levels of Insulin/ACTH, we struggle to tell if it is from stress or stress and Insulin Resistance/Cushings together.  If Insulin/ACTH levels are sky high, it is probably stress and disease.  Owners need to be aware of this limitation of tests in certain situations— if you know and we know, we will be a better team.
3.   Tell the doctor if the horse is on medications.  Certain items like Bute and Banamine will lower thyroid blood levels causing false low results.

C.    Test #1:  Insulin and Glucose

1.   When to test?

Test insulin in the morning.

  a.    In the morning, approximately 2 hours after feeding some sweet feed. Example:  Feed at 8:00 AM, test at 10:00 AM. This is a "soft" challenge and will not cause a problem.
  b.     If you have already tested Insulin, by feeding hay or low carb grain and hay, and the result is over 60, you do not need a "soft" sweet feed challenge. You are a confirmed Insulin Resistance horse already. You need to get on a program quickly to get the number down quickly.

2.   What to feed prior to the test?

a.   Hay/Fresh Grass – feed normal amount of hay you usually give in the morning.  Turn out normally onto grass after you give the sweet feed.  Put muzzle on if usually muzzle or leave off if usually you do not put on.  We will test 2 hours later.
b.   Sweet Feed - If you feed little/no grain or a low carbohydrate grain, today you will feed a very small amount of sweet feed (like Omelene 200) 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.

1000 pound horse       - Feed 4 cups
Large Pony                  - Feed 3 cups
Small Pony                  - Feed 2 cups

Cup to use is a kitchen measuring cup used in baking.  Not a scoop, not a coffee can, not a Snoopy coffee cup.

c.   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 they only feed hay to Insulin Resistance horses, their Insulin levels are the same as the normal control horses - again, a false negative. When they gave these horses 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.

3.   How to Test Insulin.

a.   Special Tubes – Several types will provide valid information, many others will cause false results.  Often, labs send doctors expired blood tubes.  All tubes have an expiration date.  We found that expired tubes draw up to 20% less blood into the tube than current tubes.  Look at the tube to make sure it is Ok. You can use serum or plasma from EDTA, but serum is best because serum is also needed to test Glucose and Thyroid levels.

Use any one of these tubes:
10ml plain red top serum tube with additive made of plastic with conventional stopper. To order tubes: Fisher Scientific: fisherhealthcare.com or 800-640-0670. Brand: BD Vaccutainer - MFG #366441, Catalog number: 02-683-60.
10ml plain red top serum tube with no additive made of glass with conventional stopper. To order tubes: Fisher Scientific: fisherhealthcare.com or 800-640-0670. Brand: BD Vaccutainer - MFG #367820, Catalog number: 02-685-112.

All of these provide serum.

Do NOT use these tubes:
Tiger top SST tubes (have gel at bottom) cause false elevations
Green, gray, and blue tops.

You will be pulling only 2 tubes to run 4 tests, but need to first use the red top tube and after that, use a purple top tube for the ACTH.  Red is first.  The tubes must be filled fully— blood will pour into the tube and at the end drip drops of blood— after drips stop, it is full.  Now, gently roll tube 8 times— required by blood tube manufacturing company.

b.   Next, you will place tubes in a refrigerator pack to cool down for 30 minutes and coagulate.  Start stop watch function on your wrist watch after blood is drawn.  Keep tubes upright in refrigerator and not on side.

c.   Next, centrifuge blood at about 3,000 rpm/5 minutes— slower rates will also work, but this is what we use in our practice.  The centrifuge is in the car— an adapter to your car’s cell phone charger part will allow plenty of power for the centrifuge.

Spinning needs to be at 30 minutes— doing it 4-6 hours later at the lab is no good and not the standard used in endocrine labs or for diabetes screening because it causes false low results.  If done correctly, Glucose levels will be over 80 mg/dl to about 100 in most horses.  If you have Glucose levels of 65, 52, 47…, then the blood was not handled properly  Glucose was eaten by red cells in the tube which will also throw off Insulin levels.  If we want accurate information and treatment, it does not start with a Glucose of 52— if we are going to test, we need to do it correctly.

d.   The serum is harvested after centrifugation into a hard plastic tube using a sterile plastic pipette.  The hard plastic tube will have a screw on top or snap-on top of hard plastic.  Why this?  The rubber top of blood tubes used to pull blood will alter results— this is why we do not harvest and put serum into another blood collection tube.  Also, the activator of the original blood collection tube can alter results if serum is exposed a second time to activator.  We learned this the hard way— it turns serum into a hard Jell-o and, again, alters results.  You only need 2cc of serum.  Next, store the serum in the refrigerator until ready to ship to lab.

e.   WARNING —  Never give your horse a shot of Insulin to see how he responds.  This is called an Insulin Challenge Test and can lead to severe laminitis or death.  If this is ever mentioned as a way to diagnose Insulin Resistance, run for the hills.

D.        Test #2 – Thyroid Hormone Levels
The red top tube and serum collected for Insulin and Glucose is enough to also test the thyroid level.  This one blood tube yields 3 results: Insulin, Glucose, and Thyroid.  Consult your doctor to see if they want to use TRH or TSH stimulation tests for thyroid levels.

E.         Test #3 – ACTH

1.   After you draw the 10cc red top, next draw blood into a 10cc purple EDTA tube to test for ACTH.
Tube to Use: 10 ml Purple Top Tube with EDTA (K3) Additive made of glass with conventional stopper. These can be ordered from Butler Animal Health, 1-800-551-3861. Manufacturer: Kendall Monoject, MFG # 8881-3117743.
2.   Like Insulin, ACTH peaks in the morning, so you need to test then. (Same time as Insulin).
3.   Like with the Insulin red top, fully fill a current-dated tube, spin at 30 minutes, harvest, put in a separate hard-plastic tube, and refrigerate.  This tube must be frozen within 2 hours of sampling and will be sent to the lab with the serum of Insulin/Glucose/Thyroid test in a refrigerator pack.  Like the previous test, only need 2cc of fluid (plasma).
4.   Cortisol testing is of no value in testing for Cushings— too variable.

Why?.
In multiple references this test is described as: "Not Definitive", "Too variable", and the test has a "lack of consistency".
Equine Internal Medicine- 2004
Equine Medicine and Surgery volume 2. 5Th Edition- 1995
Journal of Vet. Internal Medicine - 1996

5.  Do not test ACTH from August through December - is a seasonal elevation in all horses and it will cause a false reading. Spring is a good time to test.
6.   You do not need a Dexamethasone stimulation test to diagnose Cushings.

Big Point of View:  When pulling blood from horse, first pull red top, second pull purple top.  The refrigerator pack will have 2 tubes sent to the lab, one of which is frozen.

7.   Recent university project showed that all horses over 13 years old in their study had Pituitary Gland Hyperplasia, with many having high ACTH levels but no signs (laminitis, lots of hair…) yet.  This study is important because these sub-clinical “hidden” cases will also hide Insulin Resistance cases in those with both diseases.  Again, if high Insulin, test ACTH, and if high ACTH, test Insulin.

F.      Results:

1.   Insulin and Glucose. Once get to lab, Glucose results in 1 day, Insulin results in 2 days.

a.   Normally after a meal, Insulin levels of baseline 5-20 u/U/ml will go up about 40-50.  When levels are above 60, this is abnormal.  We have had several over 400 which is slam dunk Insulin Resistance.  If over 60, you are Insulin Resistant. Some labs use pmol/L for Insulin - if so, divide this number by 7.175 to get to u/U/ml.
b.   Glucose – Normally and in most Insulin Resistance horses, 80-100 mg/dl..  In very rare cases of early-stage Type II Diabetes, over 200.  If your lab uses mmol/L as Glucose unit, divide this number by .055 to get to mg/dl.
c. Glucose Insulin ratios are of little value because Insulin Resistance Horses have normal Glucose ranges. High Glucose is very rare and low Glucose from improper testing procedures throw off this ratio. Do not count on this too heavily as a diagnostic tool.

Here is an example of why it is not helpful.
Glucose levels are considered normal between 80 and 120.

Horse A- glucose of 80, insulin of 40 has a 2:1 ratio.
Horse B- glucose of 120 and an insulin of 30 has a 4:1 ratio.

Both horses are normal but ratios are double on Horse B.

Conclusion: Ratios are not going to find a problem. You know if the Insulin is over 60 there is a problem of Insulin Resistance and you know if the glucose is 40 the sample was handled poorly. Also you will know that if the glucose is sky high, your horse is Early Stage Type II Diabetic and quickly needs help. It is straight forward to diagnose and monitor progress.

2.   Thyroid – consult doctor.  Once at lab, results in 1 day.

3.   ACTH – once at lab, results in 2 days.  Normally, most horses are under 35 pg/ml.

a.   In the fall, normal horses have elevated levels in our findings of about 75-100, but studies say it can get up to 200.
b.   In the fall, you are looking for extreme ACTH elevations to diagnose Cushings of over 300.
c.   During the rest of the year, horses over 60 are suspects and usually are retested in 30 days, while horses over 100 are treated with Pergo. Our highest level: 565.  Some labs have seen levels over 1000.

G.        Retest

1.   Insulin/Glucose

a.   After 60 days on HEIRO™ Supplement and following the Insulin Resistance/Laminitis Prevention Program, retest your horse's blood. This time, you will feed the Heiro™/low carbohydrate grain/beet pulp in the morning and test the blood two (2) hours later.
b.   If you are ever concerned about the amount of grass your horse is getting, even with the muzzle, you can retest the Insulin to make sure the levels are good. For example, in April/May when starch levels double, you can turn out less (with the muzzle still on) and in June when increase turn out, you have the option of retesting. The same goes when cold weather of October comes in and stress grass sugar goes up - you can test the horse in October.
c.  Retest Insulin once a year - can do at Coggins/Vaccine time Retest at same time each year -- for example, every March.

2.   Thyroid – 2 weeks after on thyroid medicine if tested low. Adjust amount after.  Retest yearly.

3.   ACTH – 30 days after on Pergo or if monitoring to see if level is rising.  Adjust amount after.  Retest yearly.

1. What is Insulin and Insulin Resistance?
2. Exercise.
3. Chromium, Magnesium, Pergolide, Thyroid powder and Metformin
4. Diet: Best Hay, Grain, and Amounts
5. Good and bad snacks, Horse Treats
6. Avoiding Glucosamine
7. Feeding Flax Seed
8. How to correctly test for Insulin Resistance
9. Farrier Schedule/Foot Trimming/Best Glue On Shoe
10. Vaccines
11. Results

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