What Does It Mean When the Vet Wants a Glucose Curve or a Fructosamine Test?

November 02, 2026 • After the Vet Visit • All Posts • Cats • Diabetes • Dogs • Glucose Testing • Health & Wellness

By Theresa Gibilisco, owner, The Hungry Puppy

"We'd like to run a glucose curve." Or maybe it was "Let's check a fructosamine." Either way, if you have a diabetic dog or cat, you've probably heard one of these and nodded along. We hear the follow-up questions at the counter: what's the difference, and should I do anything with the food that day?

This post explains what each test shows and how it connects to the food bowl. It's general information. Your vet has the final word on your pet's testing and treatment.

What is a glucose curve?

A glucose curve is a series of blood sugar checks taken over most of a day. The blood sugar is measured before the insulin shot, then every 1 to 2 hours over about 12 hours. Put the readings on a graph and you get a curve.

That curve tells your vet three things:

The nadir. That's the lowest point of the day. It shows whether the insulin is pushing sugar too low.
How long the insulin works. If sugar climbs back up too soon, the timing or type of insulin may need a look.
How much the sugar swings. Big highs and lows matter even if the average looks fine.

What is a fructosamine test?

Fructosamine is a single blood test that reflects your pet's blood sugar control over roughly the previous 1 to 2 weeks. It forms when sugar binds to blood proteins, mainly albumin, a common protein in the blood.

What it's good for. Stress doesn't usually affect it. That helps vets tell real diabetes from a stress spike, which is common in cats at the vet.
What it can miss. Because it's an average, it doesn't show the hour-by-hour highs and lows. AAHA also notes that some well-controlled pets have a high result and some poorly controlled pets have a normal one, so trends over time mean more than a single number.
A very low result isn't automatically good news. It can mean too much insulin, or in cats, possible remission.

For cats, the international feline guidelines (ISFM) give rough bands for diabetic cats:

Fructosamine (cats)	What ISFM says it suggests
Below 350 µmol/L	Excellent control, too much insulin, or remission
350 to 450 µmol/L	Good control
450 to 550 µmol/L	Moderate control
Above 550 µmol/L	Poor control

Why would the vet want both tests?

Because they answer different questions. Fructosamine is the longer-term average. The curve shows what happens hour by hour after a shot, including dips that an average can hide.

What numbers is the vet hoping to see in a dog?

The 2026 AAHA Diabetes Management Guidelines for Dogs give these targets:

Lowest point (nadir): ideally 80 to 150 mg/dL.
Readings through the day: ideally between 80 and 300 mg/dL, and below 200 mg/dL for most of the day.
Too low: AAHA treats a reading below 60 mg/dL as low blood sugar (hypoglycemia) that calls for a dose change by your vet.

Don't panic over one high number. AAHA says that in a well-controlled dog, "occasional brief periods of significant hyperglycemia (>300 mg/dL) are expected." Hyperglycemia just means high blood sugar. AAHA describes a well-controlled dog as one without excess thirst, urination or hunger, with a stable or increasing weight.

Why don't vets do curves in the hospital for cats anymore?

Because stress at the clinic can push a cat's blood sugar up and skew the results. The 2026 AAHA cat guidelines no longer recommend in-hospital curves for routine monitoring in cats. AAHA describes stress hyperglycemia in cats as a temporary spike, usually below 250 mg/dL, that goes back to normal once the cat leaves the stressful situation. Instead, vets use blood sugar readings taken at home and continuous glucose monitors.

Dogs are different. AAHA's 2026 dog guidelines still describe in-hospital curves, and note that stress hyperglycemia in dogs is generally mild.

What's a home curve or a continuous glucose monitor?

A home curve is the same series of readings, taken by you at home on a normal day with a glucose meter. AAHA's earlier guidelines say home curves are preferred. Ask your vet whether it's an option and to show you how.

A continuous glucose monitor, or CGM, is a small sensor that checks sugar on its own. The Merck Veterinary Manual describes these sensors as reading glucose every 15 minutes for up to about two weeks. That gives your vet many days of real-life data instead of one day under stress.

Should I feed my pet normally on curve day?

Ask your vet before the appointment. AAHA's 2026 dog guidelines describe a curve that starts with a reading before the shot, then continues after a normal-sized meal and the usual insulin, and they say a dog that won't eat at the clinic can be fed and given insulin at home before coming in. Your vet's plan may differ, so ask whether to feed and give insulin at home as usual or bring the food and insulin with you, and get the answer in writing so you aren't guessing that morning.

What the sources do agree on is that the routine matters. AAHA says "consistent timing and amount of food, treats, and exercise are important" for diabetic dogs. A curve is most useful when it shows your pet's real everyday pattern.

What does this mean for the food at home?

The tests are only as useful as your routine is steady. Here's how the guidelines tie them to the food bowl:

Same food, same amount, same times. VCA says diabetic dogs "must be fed the same food in the same amount on the same schedule every day." Tufts advises keeping a cat's food and treats consistent down to brand, product and flavor.
Tell your vet before changing foods. A diet change can shift insulin needs. AAHA's 2026 dog guidelines advise "judicious initial dosing if concurrently changing the diet," and a feline veterinarian writing in AAHA's NEWStat warned that changing a cat from a high-carb diet at the same time as starting insulin "causes significant changes in glucose levels." A new curve or fructosamine after a food change is a fair question to ask.
Diabetic cats often eat very low-carb food. AAHA's target for most diabetic cats is carbohydrate below 12 to 15% of calories, ideally about 12%, with protein above 40 to 45%. Moving onto a food like that while on insulin can change a cat's glucose levels a lot, which is exactly when your vet wants numbers.
Count every treat. AAHA asks that treats and snacks be counted in the daily calories. A surprise biscuit on curve day can change the readings.
A walk after meals. For dogs, AAHA says "a walk following meals may decrease postprandial hyperglycemia," meaning the rise in sugar after eating. Keep exercise steady from day to day, since VCA names extra activity as a common cause of low blood sugar.

What is the Somogyi effect, or "rebound"?

It's when too much insulin makes blood sugar go up instead of down. Here's how AAHA's 2026 dog guidelines explain it. If insulin drops sugar too low (below 60 mg/dL) or too fast, the body fires off stress hormones such as cortisol, epinephrine (adrenaline) and glucagon. Those hormones push sugar back up high.

So a pet can look like it needs more insulin when it actually needs less. That's one big reason vets want a curve before changing a dose, and why the fix, when your vet finds rebound, is usually a lower dose. In cats, low blood sugar doesn't always trigger this rebound, and ISFM warns that raising doses too fast can cause "hypoglycaemia, rebound hyperglycaemia and poor control."

This is exactly why owners should never raise insulin on their own. AAHA says owners should "never increase the dose or frequency of insulin administration without clear instructions from their veterinarian." If your pet shows signs of low blood sugar, which AAHA lists as lethargy, sleepiness, strange behavior, abnormal gait, weakness, tremors, collapse and seizures, go to your vet or an emergency clinic now.

Can I just use urine strips instead?

Not for adjusting insulin. AAHA's 2026 cat guidelines say urine glucose is useful only occasionally and "is not a recommended routine monitoring tool." A negative strip only tells you sugar was below the level where it spills into urine, not how low it went. Ask your vet whether they want you to use them at all.

What words might I hear?

BGC: blood glucose curve.
Nadir: the lowest blood sugar reading of the day.
Hypoglycemia / hyperglycemia: blood sugar too low / too high.
CGM: continuous glucose monitor, a small sensor that reads sugar around the clock.
Glucosuria: sugar in the urine.
Stress hyperglycemia: a temporary sugar spike from stress, common in cats at the clinic.
Somogyi effect: high sugar that rebounds after a low.

What should I ask my vet?

Do you want a curve, a fructosamine, or both, and why?
Should I feed and give insulin at home that morning, or bring the food and insulin with me?
Could we do a home curve or use a continuous glucose monitor instead?
What nadir are you aiming for with my pet?
If I'm changing foods, when should we recheck?
What's our written plan if I see signs of low blood sugar?

Where to go from here

If your dog's numbers are steady and you want to fine-tune the routine, read feeding a diabetic dog around insulin shots and how to switch a diabetic dog to a new food safely. Cat owners whose fructosamine came back very low should see what diabetic remission means. For a list of diet questions, see questions to ask your vet about your diabetic dog's diet.

Prescription diets need your vet's authorization, and we're happy to reach out to your vet for you. Our own trucks deliver free on each town's route day, Tuesday through Friday, with a $20 minimum. Find your day on our local delivery page, or call 732-938-4470. For a sit-down conversation about your pet's food, book a free 45-minute Personal Pet Consultant appointment.

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