I have an older (27 yo) horse with Cushings. When the vet was here in November for fall shots I talked to her about retesting (to see if the Prascend dosage needed to be adjusted). She said to wait until January.
My other horse has Insulin Resistance, which is now under control with InsulinWise. The vet said she is happy with test results under 40, and very rarely sees horses with test results under 10.
My gelding, as a 3YO, still managed to have a run in with spring/grass induced laminitis WITH a grazing muzzle. I can tell you, you do NOT want to go through that. We were lucky and it was mild, no rotation, and he was back to light work in a few months.
Seeing your horse in that much pain and discomfort…just because “they live for grass” sure isn’t worth the risk to me. He now exists quite happily on a dry lot and I’m an extra mean mom that won’t let him hand graze either. NOT worth the risk.
We did insulin testing last fall and he came in at a 25 and T4 at 1.39. I need to read up more on the ECIR recommendations. As far as the vet was concerned that was fine, but I didn’t realize that above 10 is still a red flag (thanks @MorganMaresVT)!! We were going to do the oral sugar test next time the vet is out, but if there is better testing to get a fuller picture, I’d like to do that too.
Regardless, after the laminitis, I treat him like he’s IR/metabolic to hopefully push that day off as long as possible.
Fair enough, but I’ve owned this horse for her entire life and she’s been in this climate for 11 years (previously in Florida on grass). The ulcer/mental health risk (she tends to be a stress ball) isn’t worth it for the incredibly slight risk that she might get laminitis. 
Correct!
The baseline insulin number is high. Not scary high but high. If horse is borderline PPID but is IR, that could explain the lethargy.
I’m really curious what makes you say 25, with a ref range of 10-40, after a grain meal, is high?
I had my horse tested recently and he was not fasted (although it was not very soon after his morning RB), and I was told by internal medicine who interpreted the results that 26 (his number) was high, with the reference range given to me being normal at 4-8. Same units. We then did the glucose challenge which showed insulin response to be very dysregulated (very high including after 90min).
ETA - The guidelines they were following said that values 20-50 are suggestive of ID if there are other clinical signs.
I’d do the TRH test sooner and go from there. I can dig for my gelding’s original TRH test results from when he was diagnosed with PPID in December 2020 - the baseline value was positive and the post TRH stimulant test was overwhelmingly positive.
Prascend truly has a magical effect, or at least did for my horse, where all of a sudden he was bright, energetic, and a bit exuberant after a few days on 1/2 tab. He remains on 1/2 tab, and is doing amazing at 25 - however, I had requested that he be tested years before 2020, and the only vet I had access to at the time refused. I moved, had greater access to veterinary care, but the damage of untreated PPID had already been done. My horse developed EOTRH, has lost one tooth, has a few that will be extracted in the new year, and is clearly hurting.
I would do the TRH test and start medication if your horse is symptomatic ASAP. There are too many huge issues that can develop with untreated PPID, and I’d want to get ahead of it as quickly as possible.
My vet didn’t use the TRH method, and I had my old horse tested yearly. He felt the risk was high for inducing laminitis. We tested acth, lepitn and glucose and went from there. We always fasted.
I’m glad you mentioned this, I was going to ask my vet about the risks (if any) of the TRH test. Do you know why there’s a risk of laminitis?
@JB any thoughts on the risks?
I’ve never heard any reference to the TRH Stim test increasing the risk of laminitis. That doesn’t mean it doesn’t, I just haven’t run across it in my research
They use a steroid for the test, steriods on a horse with potential EMS or Cushings could cause it. My mare is a bit portly and even with her allergy issues we don’t use steriods to get her itching under control.
TRH Stim isn’t using a steroid, it’s a hormone - Thyrotropin releasing hormone - which stimulates the body to release more ACTH, and is a naturally occurring hormone anyway.
The dexamethasone suppression test is an old, outdated, no longer recommended at all, test that is a steroid (dex)
JB, Thank you for the correction
Update; TRH stim test scheduled for 1/6. Also testing vit E/selenium levels because what the heck.
Can’t decide if I want it to be really positive or really negative for PPID 
🤦🏻
If it makes you feel better…my gelding had very similar test results. His main issue was exercise intolerance. We put him on 1/2 tablet of prascend. He’s been on that a little over a year and he is completely back to his old self, looks great and is doing super. So finding and treating can turn out okay!
It is so valuable to have an answer.
If it makes you feel better, by the time I found a vet to take my seriously, my gelding’s post TRH result was 1150+. The vet was shocked, but 1/2 tab of Prascend a day has transformed him to a different, happier animal. He’s turning 26 this year and is vibrant, energized, and happy.
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