Help me understand thyroid results

[awaywego]

Looking for some help understanding my mare’s recent bloodwork results. My vet is a solo practitioner having his own medical issues right now, so I haven’t been able to discuss with him.

We did the testing for this 10 year old mare because while she shed out beautifully in March, she grew a coat back by June. She is neither an easy nor hard keeper.

    Free T4 by dialysis  0.62 ng/dL (Ref Interval 1.2-1.8)
    Insulin Baseline Equine 24.63 ulU/mL (Ref. Interval 10.00-40.00)
    T3 (Triiodothyronine) baseline 78.6 ng/dL (Ref. Interval 30-80)
    T4 (Thyroxine) Immulite 0.162 ug/dL (Ref Interval 1-3)

From what I have read from the Cornell site on interpreting thyroid testing, these results are indicative of primary hypothyroidism (early stage). The glucose (96, ref interval of 71-122) and ACTH (10.8 pg/ML for ACTH with a ref interval of 2-30) results were very much in the middle of the normal range.

Am I correct to understand that she is basically pre-PPID?

[JB]

Primary hypothyroidism is all but unheard of in horses, with most causes of it being EMS/IR

Equine Metabolic Syndrome (EMS) Calculator

I wasn’t sure of the unit of measure of the glucose, but you can plug numbers into the calculator and then read what means what based on the ratio which is as important as, if not more than, each number itself (glucose and insulin)

What test was done for that ACTH result, and what date?

[awaywego]

Yeah, I read the same thing about primary hypothyroidism being rare - but this is also a mare who had an ovariectomy, which 1) makes her rare, and 2) has had her hormone levels unnaturally altered.

It wasn’t a stim test for the ACTH result - I don’t know what it would be called. It was done in early June, early morning before breakfast/pasture only. I understand ideally it would have been done in May or earlier, but June was when the hair growth became apparent. I think it’s strange because she shed out very well in March and my experience is that they just don’t shed out at all vs shedding and growing back. But again, she is already weird.

I’ll take a look at the ECIR group site, thank you.

[JB]

Ok, so the other non-Stim test is the endogenous ACTH test. It’s not recommended to do that between Dec and end of June, as it can result in false negatives. That said, 10 is not likely to indicate PPID. If you want to be a lot more sure, re-test mid-Sept to mid-Oct, which is the peak of the seasonal rise