Accuracy in insulin tests between Oral Sugar Test and simple blood pull?

[twostinkydogs]

I have a call into my vet but I would be grateful for similar experiences or insights in the meantime.

My 17 y/o Andalusian mare had a simple blood test (no fasting) last month and I just received the results that show a baseline insulin of 72 ulU/ml (reference range 10-40). ACTH was normal and Leptin was 22 ng/ml (reference range 1-10).

In early 2021, she had a full fasting metabolic workup and her OST insulin results were normal both pre- and post-, normal ACTH , and Leptin was 26 ng/ml.

Both the 2021 and 2022 blood samples went to Cornell. Would another full fasting metabolic workup using OST method yield the more accurate results? I’ve already scheduled one, I am just anxiously trying to figure out if there is any chance the recent non-fasting test result is less accurate. Her pasture is very rich this year. She wears a GG muzzle 24/7 and is in work 6 days/week.

[JB]

A full fast isn’t what horses should be tested against, since they need to eat 16+ hours a day.

The only “fast” should be no concentrates, but they should have their normal forage.

An insulin reading of 72 while on grass and muzzled is a concern for sure. Leptin being 22 on top of that is very concerning.

A full fast can lead to a false negative for being IR

Some feel the cutoff of 30, not 20, for a non-fasted test is a good indicator. Others disagree

Here’s a very good read on the various setups and tests.
Testing Insulin - The Laminitis Site

[twostinkydogs]

Thank you! I definitely want to understand testing for now and the future. Off to read now. She sees the vet again next week.