Equine Insulin Testing: A Practical Guide to Insulin Dysregulation

Insulin testing is an important part of investigating insulin dysregulation (ID) in horses and ponies. ID is closely associated with equine metabolic syndrome (EMS) and is a major risk factor for endocrinopathic laminitis. When interpreted alongside the horse’s history, physical examination, diet, body condition and laminitis history, insulin results can help veterinarians identify metabolic concerns and plan appropriate follow-up.

Insulin results are not interpreted in isolation. The sampling conditions, the type of test performed and the laboratory method all influence how a result should be understood. This guide outlines common clinical reasons for testing, the difference between basal and dynamic testing, and practical considerations for equine practices.

Why measure insulin in horses?

Insulin helps regulate blood glucose and nutrient storage. In insulin-dysregulated horses, insulin concentrations may be abnormally high at rest or may rise excessively after consuming sugar or other non-structural carbohydrates. Persistent or exaggerated hyperinsulinaemia is clinically important because it is associated with an increased risk of endocrinopathic laminitis.

A veterinarian may consider insulin testing when a horse has one or more of the following:

·         Previous, recurrent or unexplained laminitis, particularly where an endocrine contribution is suspected.

·         Generalised obesity, regional fat deposits, or a prominent or cresty neck.

·         A history or examination findings that raise concern for equine metabolic syndrome (EMS).

·         A need to investigate insulin dysregulation even when outward signs are subtle.

·         A need to monitor metabolic status over time, alongside clinical findings and management changes.

A horse’s appearance alone cannot reliably confirm or exclude insulin dysregulation. Objective testing should be selected by the attending veterinarian based on the individual case.

Basal insulin testing and dynamic testing: what is the difference?

Basal (resting) insulin measures the insulin concentration in a blood sample collected under defined conditions. It is relatively straightforward, but a normal basal result does not exclude insulin dysregulation in every horse. Dynamic tests assess the insulin response after a controlled oral sugar or glucose challenge, or assess tissue response to administered insulin. These tests answer different clinical questions and should be performed using a recognised protocol.

Basal or resting insulin

Resting insulin can be a useful first step, particularly when hyperinsulinaemia is present. The veterinarian should document the horse’s feeding status, recent exercise, stress, pain, illness and medications where relevant. Recent feeding and other physiological factors can affect results, so the sampling protocol should be chosen before the sample is collected.

Oral sugar test (OST) and other dynamic tests

An oral sugar test evaluates the insulin response after administration of a defined amount of sugar under a specified protocol. Blood is collected at the protocol-defined time point or time points. Dynamic testing may identify an exaggerated insulin response that is not apparent from a single resting measurement. The exact protocol, dose, sampling time and interpretation must follow current veterinary guidance and the laboratory method being used.

Insulin tolerance tests and combined glucose-insulin tests assess different aspects of insulin sensitivity and require appropriate veterinary supervision. They are not interchangeable with a basal insulin measurement or an oral sugar test.

Why assay method and reference limits matter

Insulin assays are not necessarily interchangeable. Published thresholds can depend on the analytical method, sample type, challenge protocol and sampling time. A cut-off validated for one assay or protocol should not automatically be applied to another. Use the reference intervals and interpretive criteria supplied by the laboratory or assay manufacturer for the method actually used, and interpret the result in its clinical context.

For this reason, this article does not provide a universal insulin cut-off for all horses or all analysers. A veterinarian should confirm current method-specific thresholds before making clinical decisions.

Insulin dysregulation, EMS and PPID

EMS and pituitary pars intermedia dysfunction (PPID) are distinct conditions, but they can coexist. Some horses with PPID also have insulin dysregulation, and laminitis may occur in horses with either or both conditions. Insulin testing does not diagnose PPID; when clinical signs or age raise concern, the veterinarian may recommend appropriate ACTH-based testing in parallel or as part of a broader work-up.

The diagnosis and management plan should integrate clinical examination, history, endocrine test results and assessment of laminitis risk. Diet, forage management, exercise where appropriate, hoof care and follow-up are typically important parts of long-term management, under veterinary guidance.

Using insulin results for follow-up

Repeat testing may help the veterinarian assess metabolic status over time, but comparisons are most meaningful when sampling conditions, test protocols and analytical methods are consistent. A change in insulin concentration should be considered alongside diet and management changes, body condition, clinical signs and laminitis history.

·         Record the assay/method and the sample type used.

·         Document feeding and challenge-test conditions, including timing.

·         Use the correct sampling time for any dynamic protocol.

·         Compare results using method-appropriate reference limits.

·         Review unexpected or discordant results with the laboratory and the attending veterinarian.

In-house equine insulin testing with the BIODX HV-FIA 3000

BIODX supplies the Healvet HV-FIA 3000 veterinary immunofluorescence analyser, which the manufacturer lists with an equine insulin (eINS) assay. The supplied Healvet product information describes the eINS assay for serum or plasma, with a sample volume of 75 μL and an approximate assay time of 15 minutes. These details must be checked against the current Australian-market instructions for use (IFU), kit packaging and the exact configuration supplied before publication or clinical use.

An in-house analyser may offer a convenient way for a practice to access selected quantitative test results without sending every sample to an external laboratory. Whether the HV-FIA 3000 assay is suitable for a particular diagnostic protocol—including basal testing or samples collected after a challenge—must be confirmed against the assay’s validated intended use and IFU. Do not assume that a test is validated for every dynamic protocol simply because the analyser measures insulin.

The attending veterinarian remains responsible for selecting the appropriate test, collecting and handling samples correctly, and interpreting results in context.

Product information: Healvet HV-FIA 3000 product page

Who may benefit from an equine insulin testing workflow?

·         Equine veterinary practices investigating laminitis and metabolic health.

·         Mixed practices managing horses alongside small-animal patients.

·         Equine hospitals and referral practices conducting endocrine investigations.

·         Horse studs and breeding operations working with their veterinarian on individual horse health programmes.

For horse owners and breeding operations, testing should be arranged and interpreted by a veterinarian. The purpose is to support an appropriate clinical assessment—not to replace examination or veterinary advice.