Equine Endocrine testing

Reference: (See LabNote 56 ‘Equine PPID and EMS testing’ for a more detailed description).

2021 Equine Endocrinology group – Pituitary Pars Intermedia Dysfunction (PPID) and

2020 Equine Endocrinology group – Recommendations for the diagnosis and treatment of equine metabolic syndrome http://sites.tufts.edu/

i. Suspected thyroid dysfunction: total T4 (test code tt4), free T4 (test code ft4d), or as a panel including both (test code tprf1).

• Requires 1 mL of frozen serum shipped with a freezer pack.  Do not collect blood into SST collection tubes.
• free T4 testing is batched weekly.

ii. Suspected pituitary pars intermedia dysfunction (PPID): glucose, insulin, ACTH - can be ordered individually or as a panel, test code cuin, “Equine PPID (Cushings) profile”.

• ACTH requires 1.0 mL of EDTA plasma, which should be separated immediately following sample collection, placed into a plastic tube labelled as plasma, frozen, and shipped with a freezer pack.  Do not send whole blood.  Note: ACTH is very heat-labile.
• For insulin and glucose, collect blood into a red-top vacutainer (do not use SST blood collection tubes), avoiding hemolysis.  Allow the sample to clot, and then centrifuge.  Transfer the serum into a leakproof tube labelled as serum.  Refrigerate or freeze, and ship with freezer packs.
• 1.5 mL of serum is required for insulin and glucose.
• Insulin testing is batched weekly.

iii. Circannual increases in equine endogenous ACTH:

• December to mid-June, endogenous ACTH concentrations >10 pmol/L may support a diagnosis of PPID in horses with the appropriate signalment and clinical signs. 
• July to mid-November, endogenous ACTH concentrations >20 pmol/L may support a diagnosis of PPID in horses with the appropriate signalment and clinical signs.
• Individual horses may have higher circannual increases in ACTH concentrations, with a return to baseline in the spring.

As with all laboratory tests, endogenous ACTH results must be interpreted in the context of age, clinical history, and physical examination findings.

iv. Suspected equine metabolic syndrome (EMS): glucose, insulin - can be ordered individually or as a panel, test code insgluc, “insulin and glucose”.

• Collect blood into a red-top vacutainer (do not use SST blood collection tubes), avoiding hemolysis.  Allow the sample to clot, and then centrifuge.  Transfer the serum into a leakproof tube labelled as serum.  Refrigerate or freeze, and ship with freezer packs.
• 1.5 mL of serum is required for insulin and glucose.
• Insulin testing is batched weekly.

• Fasting is not required, but horses should not be fed grain within 4 h prior to sampling.