Insulin in cats and dogs: paired with glucose, and insulin autoantibodies

What it shows

Beta cells of the pancreas release insulin when blood glucose rises and hold it back when glucose falls. In a healthy animal low glucose means low insulin: the body switches insulin off to protect itself from a further drop. So the key question is not “is insulin high?” but “does insulin match the glucose next to it?”

On a form you may see two lines:

• Insulin — the hormone level in serum. Laboratories usually run it as a pair with glucose from the same tube, and some list the pair as one test taken when the animal is hypoglycaemic.
• Insulin autoantibody — a qualitative test that looks for antibodies the immune system has made against the body’s own insulin. It is a rarely ordered test.

Higher than reference — what it may be a sign of

• Insulin that does not switch off when glucose is low — the main reason the test exists. Low glucose with normal or high insulin at the same moment is the pattern that makes a vet suspect an insulin-producing tumour of the pancreas (insulinoma). The finding is a strong hint, not a diagnosis: the tumour itself is looked for with imaging.
• Injected insulin — in a diabetic animal on injections, too much injected insulin is itself a known cause of low glucose; the vet takes the injection schedule into account.
• Xylitol — this sweetener makes the pancreas of dogs release insulin and can drop blood sugar.
• Insulin autoantibody positive — antibodies against insulin were found. In studies of diabetic dogs such antibodies turned up in some animals, but what they mean for a particular dog is unclear, and whether canine diabetes is autoimmune at all is still debated.

Lower than reference

Low insulin with low glucose is the expected, healthy response: the body has stopped releasing insulin. Low glucose then has other explanations — for example Addison’s disease, liver failure, sepsis, large tumours outside the pancreas or a sample that stood too long before separation. Low insulin with high glucose fits a lack of insulin, as in insulin-dependent diabetes. A negative autoantibody result means no antibodies against insulin were found in that sample.

Look at together with

• Glucose from the same sample — without it an insulin result cannot be interpreted.
• Fructosamine — average glucose over the past weeks, read alongside a single glucose value.
• Cortisol — to rule out Addison’s disease as a reason for low glucose.
• ALT, bile acids, albumin — liver function, another reason for low glucose.

Units and conversion

Insulin is reported in µIU/mL (micro-international units per millilitre; on Russian forms мкЕд/мл) or in pmol/L. One µIU/mL is about 6.9 pmol/L, so 10 µIU/mL is roughly 69 pmol/L. The app keeps the unit printed on the form and converts for the chart. Insulin autoantibodies are qualitative: the form says “positive” or “negative”, and the app stores this as text.

Reference range

The reference range is on your lab’s form, and for insulin it matters only next to the glucose of the same sample. Insulin assays and their intervals differ between laboratories, so values from two labs are not compared directly. As a guide for vets, the Merck Veterinary Manual describes canine insulinoma by blood glucose below 63 mg/dL (3.5 mmol/L) and insulin above 10 µIU/mL measured at the same time. If glucose is not low at the moment of sampling, a “normal” insulin answers nothing — the vet may repeat the pair under supervision when sugar is low.

Cats and dogs

Sources

1. Buishand F. Islet Cell Tumors in Dogs and Cats. Merck Veterinary Manual, professional version, May 2024.
2. eClinPath (Cornell University College of Veterinary Medicine). Glucose — energy metabolism.
3. Texas A&M Veterinary Medical Diagnostic Laboratory. Insulin & Glucose — Fasting 12 Hour [Referral].
4. González-Villar F, Pérez-Bravo F. Determination of autoantibodies in dogs with diabetes mellitus. Veterinary World, 2021;14(10):2694–2698.
5. Ahlgren KM, Fall T, Landegren N, et al. Lack of evidence for a role of islet autoimmunity in the aetiology of canine diabetes mellitus. PLOS ONE, 2014;9(8):e105473.