Normal blood sugar in cats and glucose in dogs

Diabetes October 29, 2026 9 min read RU EN

When I first started looking up normal blood sugar in cats, I expected a threshold: below it green, above it red. That’s not how blood works. A single reading at the clinic can be high because of stress and still not mean diabetes, while a calm 5 mmol/l at home tells you nothing about what happened overnight. In this article: which numbers actually mean something, why a single reading can’t be trusted, and how to tell a home reading from a clinic one.

In October 2025, our cat Manishka was diagnosed with diabetes. Since then we’ve been measuring her blood sugar at home, and I keep records, because without them the vet has nothing to adjust the regimen with. The full story is a separate post: Manishka’s story.

Landmarks, not a norm

There is no direct “the norm is exactly this much” answer for cats, and it’s not because data is missing — it’s the way the question itself is built. A cat’s blood sugar is a moving number: it wanders through the day, so what helps isn’t one figure but three different landmarks.

In a healthy cat fasted, blood sugar is usually around 4.5–5.5 mmol/l. For a cat on insulin the landmarks are different: the vet sets a target range for that particular animal, and it is not the same range as in a healthy cat. And a frightened cat at the clinic is a story of its own: in a scared animal blood sugar can rise to roughly 14–16 mmol/l, in some cats even higher, with no diabetes involved at all — stress hormones simply dump glucose into the blood. A few hours after the cat has calmed down, the number returns to normal.

Vets working out doses hold to one principle: it’s safer for blood sugar to run a little high than to drop too low. That doesn’t mean high blood sugar is harmless and can be ignored — it’s a rule for choosing inside treatment, under a vet’s supervision. If the numbers regularly leave the range your vet has set, that’s a reason to call them, not to inject insulin based on a picture from the internet — though a number inside the range isn’t a guarantee of wellbeing either.

Why a single reading means nothing

Blood sugar is not a constant. It rises after food, falls after insulin, and overnight it can head in any direction. One reading is one point, and you can’t judge the shape of a day from one point: a calm 6 mmol/l at noon doesn’t tell you it wasn’t dangerously low yesterday at the same hour.

That’s why a diagnosis is never made on one high reading, and why the dose must not be raised on one high reading — not by the owner, not by the vet. One low reading before the shot works the other way around: under a rule agreed with the vet in advance, insulin is skipped or a reduced dose is given in that situation. Vets explicitly recommend home monitoring instead of clinic curves: a series of readings in familiar surroundings shows what an ordinary day looks like for the animal — morning before insulin, several points during the day, the same hours for several days in a row. Then you can see whether the cat lives inside the range, spikes after the bowl, or dips too low — including before the drop becomes visible in behaviour.

There is also a test that answers the question “so what was the sugar on average” — fructosamine. It shows roughly what the blood sugar was over the previous 7–10 days, and brief stress barely affects it. That’s exactly why a vet may order it when one-off readings look dubious.

Changes to the regimen are made slowly: the dose goes up no more often than once every 5–7 days, and only on consistent signs, not on a single spike — that’s the requirement of the current consensus guidelines, and it protects against weekly rollercoasters. And there’s no getting around keeping records: a week later you can no longer remember what was before food and what was after the shot — and the appointment turns into a guessing game.

Over these months we’ve accumulated ten thousand readings, and they confirm it: a one-off reading swings more than you’d think. So I don’t compute averages from it, and I don’t take a good morning for a trend. Which symptoms and tests actually confirm the diagnosis itself, when diabetes is only suspected, is covered in the overview of diabetes in cats.

How a home reading differs from a clinic one

At the clinic they most often take venous blood after the car ride, the waiting room and being held down. At home — a drop from the ear, a familiar room, hands the cat is used to. Different method, different sample, different level of stress, so numbers from these two worlds can’t be compared head-on. Even the devices aren’t twins: a laboratory analyser and a home glucose meter can differ slightly, and that’s normal — what matters is knowing which device produced each number. I note which device each reading came from, and I bring both the numbers and the meter itself to appointments, in case the vet wants to cross-check. I keep my records in the Diabnostic logbook — they’re always at hand and easy to show the vet. For choosing a device there’s a separate post on glucose meters for cats.

The two kinds of reading mean different things. The clinic answers what is happening in that room right now; a series at home answers what an ordinary day looks like. For tuning treatment, the second is more informative.

One technical trap: some devices and lab forms report mg/dl, others mmol/l. The conversion is simple, a factor of 18: for example, 8 mmol/l is about 144 mg/dl, and 4.5 mmol/l is about 80 mg/dl. Convert the units before comparing a clinic form with your home numbers. How the drop is physically taken, and which mistakes pile up in the first month, is covered in How to measure your cat’s blood sugar at home.

Numbers that call for action right away

There is one boundary that calls for immediate action — hypoglycemia, blood sugar falling too far. Below 3.0–3.5 mmol/l is already hypoglycemia; for a home glucose meter, which can be slightly off, it’s more conservative to treat 3.5 as the danger line. This condition doesn’t wait, so if the number is below the threshold there’s no reason to sit and watch: what to do at that moment is a separate algorithm, covered in the overview of diabetes in cats.

Sugar in urine: what the strip actually tells you

Glucose appears in urine only once blood sugar has exceeded the renal threshold — the level above which the kidneys stop holding glucose back. In a cat it’s around 14–15 mmol/l; in a dog it’s lower, about 10–11. So the strip tells you the threshold was exceeded at some point, not what the number in the blood is at this minute: as long as blood sugar stays below the threshold, the urine will remain clean even if it’s elevated.

And what about dogs?

The headline promised dogs too, so briefly. A one-off clinic reading in cats can mislead badly precisely because of stress — that was covered above. In dogs the renal threshold is lower, so sugar appears in urine earlier than in a cat. And the main difference is remission: it’s an almost exclusively feline phenomenon; dogs, as a rule, need insulin long-term. More in the post on diabetes in dogs.

Sources

Sparkes AH, Cannon M, Church D, et al. ISFM Consensus Guidelines on the Practical Management of Diabetes Mellitus in Cats. J Feline Med Surg. 2015;17(3):235–250.
Taylor S, Cannon M, Church D, et al. 2025 iCatCare consensus guidelines on the diagnosis and management of diabetes mellitus in cats. J Feline Med Surg. 2025;27(11).
Bugbee A, Rucinsky R, Alvarez E, et al. 2026 AAHA Diabetes Management Guidelines for Cats. J Am Anim Hosp Assoc. 2026;62:65–93.

This text is one owner’s experience and a review of open veterinary guidelines, not a prescription. Insulin doses, choice of drug, and any changes to the regimen — only with your veterinarian.