Help me prepare for insulin and TRH / ACTH tests

[PonyRiderMom]

I moved from the city to the country, and there are far fewer vets here. When I was in the city, I had a host of equine vets to choose from, including an internal medicine specialist who was very thorough, methodical, and knowledgeable. Where I am now, I don’t really have a choice of vets. There is one practice, and like my daughter’s kindergarten teacher said, “You get what you get and you don’t throw a fit.”

All of that is to preface I want to get two of my horses re-tested for Cushings. I know one of them has it, but I’d like to see what his numbers look like. The other one may be developing it. I have asked the vet’s office for them to do the ACTH and TRH test for Cushings, and I’d like the horses’ insulin levels tested as well.

When I got them tested a few years ago, my knowledgeable vet said to just leave them on the pasture overnight, since it wasn’t much of a pasture (most of their calories came from round bales) and that was what they were used to, rather than strictly fasting them. I’ve asked my current vet’s office what I should do about fasting them. It looks like one of the insulin tests they could do requires fasting, and I will ask the same question about this.

I’m asking here because, in case my vet’s office doesn’t respond (they are really good at not responding) I’d like to know whether I should be fasting them or not, and if so how much I should fast them. My inclination is to leave them in their dry lot, but with their regular hay, overnight. No feed and no special hay in the morning. I could also leave them in their dry lot with no hay, or with a small amount of hay that they would presumably finish some time in the night. The pasture they have access to (if I don’t close it off) is not a poor pasture like it was at the old place, and they could be out there eating all night for all I know. What have people’s vets recommended in this situation?

[NaturallyHappy]

My vets recommend in with hay all night. We’ve occasionally tested after they’ve been turned out because I am insanely curious about insulin levels.

[OzarksRider]

I’ve always turned my horse out as usual before blood was drawn. He’s stalled with hay at night, gets a balancing ration with a handful of oats morning and evening, and grazes with a muzzle during the day. My vet has always ordered just ACTH and insulin (no TRH). Cornell’s lab report for insulin includes a reference range for both fasting and non fasting specimens. I wonder if you could call Cornell to ask if your horses should be fasting if you don’t hear from your vet?

[PonyRiderMom]

Haha, me too. I asked the vet last time if they can’t make something like they have for people, where you can just do a finger prick and have a test strip, and it would give you instant results. Wouldn’t that be great? You could go out there and test them literally every hour and bring them in off the pasture if their levels started going up.

[JB]

@PonyRiderMom

I want to get two of my horses re-tested for Cushings. I know one of them has it, but I’d like to see what his numbers look like.

You need the ACTH test and that can be done any time of year, non-stressed horse, and go by the normal range for that time of year. If you have to trailer the horse somewhere, you need to wait at least 30 minutes after arrival to pull blood, to allow cortisol to return to somewhat normal. Ideal though is on-farm blood pull

@PonyRiderMom

The other one may be developing it. I have asked the vet’s office for them to do the ACTH and TRH test for Cushings, and I’d like the horses’ insulin levels tested as well.

TRH can only be done Jan through end of June, maybe mid-December. Other months don’t have enough data to properly interpret results. The seasonal rise is in full swing now, peaking mid-Sept to mid-Oct in the northern hemisphere, making it the ideal time for a first test, as even early PPID horses tend to have an higher than normal rise. TRH is more sensitive, seeing earlier PPID better than any ACTH test, but you can’t do it now

**add 6 months if you’re in the Southern hemisphere

@PonyRiderMom

I’d like the horses’ insulin levels tested as well.

forage-only fast, NO concentrates, for 12 hours before. It may actually be more like 4-8, but 12 is safe. And, you need the glucose number AND you need to look at the ratio of the 2

Equine Metabolic Syndrome (EMS) Calculator

@PonyRiderMom

When I got them tested a few years ago, my knowledgeable vet said to just leave them on the pasture overnight, since it wasn’t much of a pasture (most of their calories came from round bales) and that was what they were used to, rather than strictly fasting them. I’ve asked my current vet’s office what I should do about fasting them. It looks like one of the insulin tests they could do requires fasting, and I will ask the same question about this.

see above - forage-only “fasting”, whatever their normal forage schedule is

[NaturallyHappy]

@PonyRiderMom

Haha, me too. I asked the vet last time if they can’t make something like they have for people, where you can just do a finger prick and have a test strip, and it would give you instant results. Wouldn’t that be great? You could go out there and test them literally every hour and bring them in off the pasture if their levels started going up.

We need a support group!. Oh wait - we have it.

[OzarksRider]

@JB

go by the normal range for that time of year.

Just curious . . . where can I find the normal ranges for the time of year? The lab report I get doesn’t specify ranges for the time of year. The notes on the report just say that ACTH results in normal horses may be up to 4 times the reference range during the seasonal rise, which the report says is August through October.

[JB]

@OzarksRider

The lab report I get doesn’t specify ranges for the time of year.

what lab is being used? That’s not cool to not list the reference ranges

Reference-Ranges-for-Evaluation.pdf

[OzarksRider]

Thanks for the info. My vet uses the lab at Cornell University School of Veterinary Medicine. Their reference interval for ACTH is 2-30 pg/mL. The interpretive notes for the test caution that the results for normal horses can be up to 4 times this much during the seasonal rise August-October. I don’t know if they use a different reference interval during the seasonal rise because my horse has only been tested March-June.

[JB]

Yes, they list different ranges based on the time of year. Mid-March to mid-April is the “peak” of the seasonal low