VetVaultCat diabetes blood tests: glucose, fructosamine and monitoring
Vets diagnose diabetes in a cat when blood glucose stays high and glucose appears in the urine, usually confirmed by a raised fructosamine, in a cat that drinks and urinates more, loses weight and is often hungrier. A single high glucose at the clinic is not enough: stress alone can push a cat's blood sugar far above the range.
Cat diabetes tests at a glance
| Test and what it measures | Main use | Main limits |
|---|---|---|
| Blood glucose – sugar in the blood at that moment; roughly 70–150 mg/dL (about 3.9–8.3 mmol/L) in healthy cats | Diagnosis, curves, spot checks | Stress can raise it a lot |
| Urine glucose – appears once blood glucose passes the kidney threshold, roughly 270 mg/dL (15 mmol/L) in cats | Diagnosis, home monitoring | Most treated cats still have some |
| Ketones (urine strip or blood BHB) – made when the body burns fat instead of glucose | Detecting DKA | Urine strips can miss early ketosis |
| Fructosamine – average glucose over roughly the previous 1–3 weeks | Diabetes versus stress, trends | Misses brief lows |
| Glucose curve or CGM – glucose over a day or several days | Judging treatment | Clinic curves distorted by stress |
Always use the range on your own report. Ranges differ between laboratories, analyzers and glucose meters. To convert glucose from mg/dL to mmol/L, divide by 18.
How vets diagnose diabetes in cats
Most diabetic cats are middle-aged or older; overweight cats, male cats and cats on steroids are at higher risk. Classic signs are drinking and urinating more, weight loss despite a good or increased appetite, and sometimes weak back legs with the hocks dropping toward the ground, caused by nerve damage.
The laboratory picture is persistent hyperglycemia (high blood glucose) plus glucosuria (glucose in the urine), supported by a raised fructosamine. Current AAHA guidance for cats stresses evidence of sustained hyperglycemia, and the 2025 International Cat Care (iCatCare) guidelines use criteria agreed by the ALIVE project:
| Random blood glucose | Also needed |
|---|---|
| 270 mg/dL (15 mmol/L) or higher | Classic signs, plus a raised fructosamine or glucosuria on more than one home-collected urine sample |
| Above 126 and up to 270 mg/dL (7–15 mmol/L) | At least two of: classic signs; raised fructosamine; glucosuria on more than one home-collected urine sample |
Home urine samples should be collected at least two days after any stressful event.
Stress hyperglycemia: high blood sugar without diabetes
In a frightened cat, stress hormones quickly release glucose into the blood; a car ride and a blood draw can be enough. The iCatCare guidelines note that stress hyperglycemia can be of any magnitude, so even a very high clinic glucose does not prove diabetes. Vets tell the two apart with:
- fructosamine, which brief stress barely moves;
- urine glucose on a sample collected at home with non-absorbent litter;
- glucose measured at home or with a CGM sensor;
- clinical signs – stress does not cause weeks of thirst and weight loss.
If the picture is unclear, vets usually recheck later rather than start lifelong treatment on one result.
What fructosamine shows, and its limits
Fructosamine forms when glucose sticks to blood proteins, mainly albumin. It reflects average glucose over roughly the previous one to three weeks; in cats, mostly the last one to two. Its blind spots:
- Hyperthyroidism and low blood proteins (for example protein loss through the gut) make it falsely low, which can hide diabetes.
- It can still be normal in early diabetes.
- It does not show short episodes of low glucose, so a high result does not rule out hypoglycemia between doses.
- Hemolysis (burst red cells in the sample) shifts it unpredictably.
Cut-offs for "good control" are not well established in cats, so vets compare results over time. A normal fructosamine in a cat on insulin can signal remission or a risk of low blood sugar: a reason for your vet to review treatment, not for you to change it. See where both fit on a full panel in cat bloodwork explained.
Monitoring a diabetic cat: curves, CGM, urine and fructosamine
Many diabetic cats receive insulin injections, usually twice a day. Some otherwise healthy, newly diagnosed cats instead take a once-daily oral SGLT2 inhibitor (bexagliflozin or velagliflozin). Your vet sets the monitoring plan, and how your cat is doing day to day matters as much as the numbers. A daily diary of thirst, appetite, weight and energy is valuable.
Blood glucose curves
A curve is a series of readings across the day, usually just before the morning insulin dose and then about every two hours until the evening dose. Your vet reads it for:
- nadir – the lowest point and when it occurs, showing the insulin's strongest effect and whether glucose dips too low;
- duration – how long glucose stays lower before climbing again, showing whether insulin type and timing suit your cat;
- overall level and swings across the day.
Curves done at the clinic can be distorted by stress, so many vets now prefer home curves or a continuous glucose monitor for cats. Many owners do curves at home from a drop of blood at the ear edge, using the meter their vet recommends; meters made for people often read lower in cats.
Continuous glucose monitors
A CGM sensor is a small disc on the neck, chest or back that reads glucose under the skin every few minutes for up to about two weeks and sends data to a phone the clinic can review. It catches lows a home curve can miss, but is less accurate at low values.
Urine strips and fructosamine
Dipsticks on urine collected at home show glucose and ketones. Most treated cats still have some urine glucose, so doses are not adjusted on it. A negative glucose result can be an early sign of remission, and any ketones need a call to your vet, especially in the first weeks of SGLT2 inhibitor treatment. Fructosamine rechecks show the longer trend between visits.
Emergencies: low blood sugar and ketoacidosis
Ask your vet for a written emergency plan when treatment starts.
Hypoglycemia (blood sugar too low) – act now. It is usually caused by insulin, for example too large a dose, a missed meal or a cat moving toward remission. Signs include:
- weakness, lethargy or unusual quietness;
- wobbliness or walking as if drunk;
- trembling or twitching;
- seizures, collapse or unconsciousness.
Follow the emergency plan your vet gave you and go to a vet immediately. Do not pour anything into the mouth of a cat that is seizing or unconscious. Do not give the next insulin dose until a vet has advised you, and never give insulin to a cat that is not eating without your vet's guidance.
Diabetic ketoacidosis (DKA) is an emergency. When cells cannot use glucose, the body breaks down fat into acidic ketones. DKA can be how diabetes is first found or can develop during treatment. Go to a vet or emergency clinic immediately if a diabetic cat:
- eats less or stops eating;
- vomits;
- is lethargic or weak;
- seems dehydrated (dry, tacky gums);
- breathes fast.
In cats on SGLT2 inhibitors, DKA can develop even when glucose is not very high (euglycemic DKA). Never change an insulin dose without your vet.
Diabetic remission in cats
Unlike dogs, many diabetic cats go into remission: their own insulin production recovers and they no longer need treatment. ALIVE defines remission as at least four weeks without insulin and without signs. Reported rates vary widely, from about 11% to over 60% of cats in different studies according to the 2025 iCatCare guidelines, and Cornell's Feline Health Center notes that a cat not in remission within about six months will most likely need lifelong treatment. Remission is more likely with:
- early diagnosis and prompt treatment;
- good glycemic control reached quickly;
- a low-carbohydrate diet, usually wet food, chosen with your vet;
- slow, supervised weight loss in overweight cats;
- stopping diabetes-promoting drugs such as steroids, where possible.
A low-carbohydrate diet can lower insulin needs, so plan diet changes with your vet. Negative urine glucose, lower curve or CGM readings, a normal fructosamine or a low-sugar episode can all mean remission is starting: contact your vet promptly. Diabetes can return, so cats in remission still need monitoring.
Other tests in diabetic cats
| Test | Why it matters |
|---|---|
| CBC and chemistry panel | Overall health, dehydration, other disease; potassium and phosphorus often fall in DKA. |
| Urinalysis, plus culture if infection is suspected | Glucose, ketones and signs of infection; diabetic cats are more prone to bladder infections. |
| Blood BHB | Detects ketosis earlier than urine strips; checked around SGLT2 inhibitor treatment. |
| Liver values (ALT, ALP) | Mild rises are common in diabetes; large rises in a cat not eating suggest fatty liver (hepatic lipidosis). |
| Kidney values | Chronic kidney disease often coexists and can change diet choices. See cat kidney values. |
| Total T4 | Hyperthyroidism causes similar weight loss and lowers fructosamine. See cat thyroid T4. |
| Pancreatic lipase (fPLI) | Pancreatitis often accompanies diabetes and raises DKA risk; mild rises are common, so results are read with symptoms. |
| IGF-1 | Screens for acromegaly (hypersomatotropism), a pituitary tumor causing insulin resistance. |
Questions to ask your vet
- Which results confirm diabetes, and could stress explain any of them?
- Could thyroid or protein levels affect my cat's fructosamine?
- Should we monitor at home with a meter, CGM sensor or urine strips?
- What is our emergency plan, and what do I do if my cat does not eat at dose time?
- Is remission realistic, and which diet and weight plan gives the best chance?
- Do we need T4, pancreatic lipase or IGF-1 tests?
Frequently asked questions
What is a normal blood glucose level for a cat?
In healthy cats it is roughly 70 to 150 mg/dL (about 3.9 to 8.3 mmol/L), but ranges differ between laboratories and meters, so use the range printed on your own report. Stress at the clinic can push a healthy cat well above this range.
Does high blood sugar always mean my cat has diabetes?
No. Cats often develop stress hyperglycemia during a vet visit, and it can be of any size. Vets confirm diabetes with signs such as increased thirst and weight loss, glucose in urine collected at home and a raised fructosamine, or with repeated high readings taken in a calm setting.
What does fructosamine show in a cat?
Fructosamine reflects the average blood glucose over roughly the previous one to three weeks, mostly the last one to two in cats. Brief stress does not raise it, but hyperthyroidism and low blood proteins can lower it falsely, and it does not show short episodes of low blood sugar.
What is a glucose curve for a cat?
It is a series of glucose readings taken across the day, usually before the morning insulin dose and then about every two hours, or recorded continuously by a sensor. Your vet uses the lowest point (nadir), how long the insulin works and how high glucose runs to judge treatment. Never change an insulin dose yourself based on a curve.
Can diabetic cats go into remission?
Yes. Many cats stop needing treatment, especially when diabetes is diagnosed early, good control is reached quickly, and they eat a low-carbohydrate diet and lose excess weight. Diabetes can return, so cats in remission still need regular checks.
What are the signs of low blood sugar in a diabetic cat?
Weakness, lethargy, wobbliness, trembling or twitching, seizures and collapse. Follow your vet's emergency plan and go to a vet immediately, and do not give more insulin until a vet has advised you.
Is diabetic ketoacidosis in cats an emergency?
Yes. A diabetic cat that stops eating, vomits, is lethargic, seems dehydrated or breathes fast needs a vet immediately. DKA is treated in hospital with fluids, insulin and close monitoring.
Sources
- Taylor S, Cannon M, Church D, et al. 2025 iCatCare consensus guidelines on the diagnosis and management of diabetes mellitus in cats. Journal of Feline Medicine and Surgery. 2025;27. doi.org/10.1177/1098612X251399103
- American Animal Hospital Association. 2026 AAHA Diabetes Management Guidelines for Cats. aaha.org/diabetes-management-cats
- Cornell Feline Health Center. Feline Diabetes. vet.cornell.edu
- International Cat Care. Diabetes mellitus in cats. icatcare.org/articles/diabetes-mellitus-in-cats
- International Cat Care. Managing the diabetic cat: a guide for caregivers (2025). icatcare.org (PDF)
- eClinPath, Cornell University College of Veterinary Medicine. Fructosamine. eclinpath.com/chemistry/energy-metabolism/fructosamine