Diabetes in Cats: Insulin Storage, Curves, and Remission

Most diabetic cats are not dependent on insulin for life in the way a type 1 human is. The disease is closer to type 2: the body still makes insulin, but the tissues stop responding to it, and the pancreas eventually tires. That matters because a cat diagnosed early, put on a low-carbohydrate diet, and dosed carefully has a real chance of coming off insulin entirely. The other thing that matters is technique, since most treatment failures at home are dosing errors, not drug failures.

Why obesity drives most cases

Fat tissue is not inert. It releases hormones that blunt the insulin signal, so the pancreas has to push out more insulin to move the same glucose into cells. That compensation fails faster in cats, whose islet cells readily deposit amyloid. Overweight cats are several times more likely to develop diabetes, and a cat at 6 kg carries meaningfully more risk than the same cat at 4.5 kg.

Signs follow the classic four: drinking more, urinating more (and larger clumps in the litter box), eating well or ravenously, and losing weight. A cat urinating outside the box or suddenly preferring the bathtub is often showing the same thing. Left untreated, the cat switches to burning fat, develops ketoacidosis, and becomes lethargic, dehydrated, and vomiting within days.

Diagnosis takes three pieces, not one

A single high blood glucose is not a diagnosis. Stress alone can push a cat's glucose from 100 to over 250 mg/dL in the clinic. Vets confirm with a combination:

• Persistently high fasting glucose on more than one occasion, ideally with water intake and urine output documented.
• Fructosamine, which reflects average glucose over the previous 1 to 3 weeks and is not thrown off by a stressful car ride.
• Urine glucose and ketones. Glucose in the urine means the level has been above the kidney threshold for a while; ketones mean the cat is heading for ketoacidosis and needs same-day care.

Diet changes the trajectory

Diet is not a nice extra; it is part of the treatment. The usual approach is high protein, low carbohydrate, and wet food rather than dry, because most dry foods sit at 30 to 45 percent carbohydrate on a dry-matter basis while pate-style cans often land under 10 percent. Many cats reach remission on diet change plus insulin, and a few manage on diet alone if caught early. See wet versus dry food and obesity and weight loss for the mechanics of the switch.

Change the food over 7 to 10 days to avoid vomiting and refusal, and feed the same amount at the same times daily, ideally timed to the injection. A cat who eats erratically cannot be dosed safely on a fixed schedule; see how often to feed a cat.

Insulin: the part people get wrong

Vets commonly use glargine, detemir, PZI, or a human isophane (NPH) insulin, all given twice daily about 12 hours apart. Dosing starts low, around 0.5 to 1 unit per cat twice daily for a typical 4 to 5 kg cat, and is adjusted only after a glucose curve, in steps of 0.5 to 1 unit at a time, no more often than every 5 to 7 days. Under-dosing for a week is far safer than over-dosing.

The syringe concentration is where serious mistakes happen. Insulin comes as U-40 (40 units per mL) or U-100 (100 units per mL), and the syringe must match. Drawing U-40 insulin into a U-100 syringe gives roughly 2.5 times the intended dose, which can kill a cat. Drawing U-100 insulin into a U-40 syringe badly under-doses. Keep one insulin and one matching box of syringes, and never borrow a syringe from a diabetic human in the house without checking the label.

Storage: unopened vials go in the fridge at 2 to 8 degrees Celsius, never the freezer. Opened vials last about 28 to 42 days depending on the product, then lose potency. Roll rather than shake, and discard anything with particles or discoloration.

How to run a home glucose curve

A curve is a series of readings across one dosing interval. In the clinic it is a long day for a stressed cat; at home it is cheaper and more accurate.

1. Feed and inject as usual at time zero.
2. Take a reading before the injection, then every 2 hours until the next dose, so 7 readings across 12 hours.
3. Note food, activity, and any odd behavior beside each number.
4. Repeat the curve every 5 to 7 days while adjusting, then every 1 to 3 months once stable.

A continuous glucose monitor (Libre-type sensor) worn on the flank gives a 24-hour trace without 7 pinpricks and is increasingly the first choice. Either way, the goal is not one perfect number but a nadir that stays above 80 to 100 mg/dL with no sharp drops.

Low blood sugar: recognize it and act

Hypoglycemia is the emergency that matters most at home. Signs run in order: restlessness or unusual quiet, weakness in the back legs, wobbling, head tremors, then seizures and collapse. Any of these after an injection means treat first, ask questions later.

Rub a teaspoon of glucose syrup, honey, or karo syrup on the gums and inner lip, not into the throat, where it can be inhaled. Wait 2 to 3 minutes. If the cat responds, offer a small meal and call the vet. If there is no response in 5 minutes, repeat once and go to the clinic. Never force food or liquid into a cat who is unresponsive.

Remission is possible, and it is not a cure

Remission means the cat maintains normal glucose without insulin. The practical definition is no insulin for 2 weeks with glucose staying in the normal range on a curve. It usually happens in the first 3 to 6 months, most often in cats whose control improved quickly and whose weight and diet changed. A cat in remission still has a damaged pancreas and needs a curve every 3 to 6 months.

Relapse is common enough to plan for. Some cats go back on insulin within a year, often after weight gain, a course of steroids, or pancreatitis. Keep the meter and the prescription food on hand.

Daily routine at a glance

Task	When	What wrong looks like
Injection	Every 12 hours, after food	Cat did not eat half the meal: skip the dose and call the vet
Weight	Weekly, same scale	Losing more than 2 percent a week
Water intake	Daily, rough count	Back to drinking heavily after weeks of normal
Glucose curve	Every 5 to 7 days while adjusting	Nadir under 80 mg/dL or a drop over 150 mg/dL

Call the clinic the same day for ketone-positive urine, repeated vomiting, refusal to eat for 24 hours, or any hypo episode that needed syrup.

Frequently asked