Diagnosing diabetes in cats requires more than a single blood test. Because cats are uniquely prone to stress-related blood sugar spikes, veterinarians use a combination of clinical signs, blood work, urine testing, and sometimes at-home monitoring to confirm a diagnosis. The process is designed to distinguish true diabetes from a temporary stress response that can look almost identical on paper.
Signs That Prompt Testing
The three hallmark signs of feline diabetes are increased urination, increased thirst, and weight loss. You might notice your cat’s litter box is heavier than usual, their water bowl empties faster, or they’re losing weight despite eating the same amount or even more than before. These changes often develop gradually over weeks, so they’re easy to miss at first.
Some cats also develop a distinctive change in how they walk. Instead of walking on their toes like cats normally do, a diabetic cat may start walking flat on their hind legs, with their ankles (hocks) sinking down to the ground. This plantigrade stance results from nerve damage caused by prolonged high blood sugar. A dull, unkempt coat is another common finding, since cats that feel unwell tend to groom less.
Why a Single Blood Sugar Reading Isn’t Enough
Here’s the complication that makes feline diabetes harder to diagnose than in dogs or humans: cats experience dramatic stress-related blood sugar spikes. A non-diabetic cat that’s anxious about a vet visit can have blood glucose levels exceeding 300 mg/dL, well into the range that would indicate diabetes in a calm animal. In a cat that actually has diabetes, stress can push readings above 500 mg/dL. These elevated levels can persist for several hours after the triggering event.
This means a single high blood glucose reading at the clinic could reflect genuine diabetes or simply a scared cat. Your vet will never diagnose diabetes on that number alone.
The Fructosamine Test
The most reliable way to separate stress spikes from true diabetes is a blood test called fructosamine. While a standard blood glucose reading captures a single moment in time, fructosamine reflects your cat’s average blood sugar over the previous 7 to 10 days. A brief stress spike at the vet won’t significantly move this number, but weeks of genuinely elevated blood sugar will.
In healthy cats, fructosamine levels typically range from about 2.1 to 3.8 mmol/L. Cats with temporary stress-related high blood sugar fall in a similar range, up to about 4.1 mmol/L. Diabetic cats, by contrast, have levels starting at 3.4 mmol/L and often exceeding 6.0 mmol/L. As a standalone test for distinguishing diabetic from non-diabetic cats, fructosamine is 92% sensitive and 96% specific, making it one of the most useful tools in the diagnostic process.
Another test that works on a similar principle measures a form of hemoglobin that reflects blood sugar levels over the lifespan of red blood cells, roughly 68 to 77 days in cats. This test is less commonly used in practice but can help in ambiguous cases.
Urine Testing
Urinalysis plays a key supporting role. When blood sugar rises above a certain threshold, the kidneys can no longer reabsorb all the glucose, and it spills into the urine. Finding glucose in the urine (glucosuria) alongside high blood sugar strengthens the case for diabetes considerably, because stress alone rarely pushes glucose into the urine for sustained periods.
Your vet will also check the urine for ketones. When the body can’t use glucose for energy, it starts breaking down fat instead, producing ketones as a byproduct. The presence of ketones in the urine, combined with high blood sugar, glucose in the urine, and signs of metabolic acidosis, points to diabetic ketoacidosis. This is a serious, potentially fatal complication that requires immediate treatment and is sometimes the crisis that leads to a diabetes diagnosis in the first place.
At-Home Monitoring
When the picture remains unclear after clinic testing, your vet may ask you to collect information at home. This can involve checking your cat’s blood sugar with a portable glucometer, using urine dipsticks to test for glucose, or in some cases, using a continuous glucose monitor. At-home data is valuable precisely because it removes the stress variable. A cat relaxing on the couch will give a much more accurate glucose reading than the same cat on a steel exam table.
The 2025 iCatCare consensus guidelines specifically acknowledge that some cases simply can’t be resolved in the clinic. When diabetes and stress hyperglycemia can’t be distinguished through standard testing, at-home monitoring and periodic re-evaluation are the recommended path forward.
Ruling Out Other Conditions
Several other diseases cause increased thirst, increased urination, and weight loss in cats, so your vet will typically run additional tests to rule them out or identify them as co-existing problems.
- Hyperthyroidism is extremely common in older cats and shares many of the same symptoms. A simple blood test measuring thyroid hormone levels can confirm or rule it out.
- Chronic kidney disease also causes increased thirst and urination. Blood work and urine concentration measurements help distinguish it from diabetes.
- Growth hormone excess (hypersomatotropism) can actually cause diabetes by making the body resistant to insulin. This condition is suspected when a diabetic cat requires unusually high doses of insulin to control blood sugar.
- Cushing’s disease involves overproduction of cortisol and contributes to insulin resistance. It’s relatively rare in cats but is tested for through cortisol suppression tests when suspected.
These conditions don’t just mimic diabetes. They can also exist alongside it and make it harder to manage. That’s why the recommended first step after a new diabetes diagnosis is to screen for complicating factors and concurrent diseases before starting treatment.
What the Diagnostic Process Looks Like
In practical terms, expect at least two vet visits. The first typically involves a physical exam, blood work (including glucose and fructosamine), and a urinalysis. If results are clear cut, with high fructosamine, glucose in the urine, and classic symptoms, your vet can diagnose diabetes and begin discussing treatment on the spot.
If the results are borderline, or if your cat was visibly stressed during the visit, your vet may recommend a waiting period with at-home monitoring before making a definitive call. This isn’t indecision. It’s appropriate caution, given how dramatically stress can distort the numbers in cats.
One thing worth knowing: feline diabetes can go into remission. Remission is defined as needing no insulin for at least four weeks with no symptoms of diabetes. This possibility is one reason getting the diagnosis right matters so much. Starting insulin in a cat that doesn’t actually have diabetes, or delaying treatment in one that does, both carry real consequences. The diagnostic process exists to thread that needle as accurately as possible.