A well-managed diabetic dog should maintain blood sugar between 80 and 200 mg/dL throughout most of the day, with the lowest point (called the nadir) ideally falling between 80 and 150 mg/dL. For comparison, a healthy non-diabetic dog has blood sugar in the range of 80 to 120 mg/dL. The goal of treatment isn’t to perfectly replicate those healthy numbers, but to keep glucose reasonably controlled while avoiding dangerous lows.
Target Range vs. Healthy Range
In a dog without diabetes, blood sugar naturally stays between 80 and 120 mg/dL. The body handles this automatically through insulin production. A diabetic dog on insulin therapy can’t regulate glucose as precisely, so veterinarians aim for a wider acceptable window: 80 to 200 mg/dL. Readings within that range throughout the day indicate good control.
The lowest point blood sugar reaches after an insulin injection is the nadir, and it’s one of the most important numbers your vet watches. The ideal nadir is 80 to 150 mg/dL. If blood sugar drops below 80, there’s a risk of hypoglycemia, which can cause weakness, trembling, seizures, or collapse. If the nadir stays above 150, the insulin dose or timing may need adjustment.
How Blood Sugar Is Tracked
The primary tool for understanding a diabetic dog’s glucose pattern is a blood glucose curve. This involves measuring blood sugar every two hours over the full interval between insulin injections, typically 12 hours for dogs receiving insulin twice daily or 24 hours for once-daily dosing. If at any point during the curve blood sugar drops below 150 mg/dL, readings should switch to every hour to catch any further drop before it becomes dangerous.
Your vet will recommend a glucose curve in several situations: after starting a new type of insulin, 7 to 14 days after any dose change, at least every three months for dogs that seem well controlled, and whenever symptoms like excessive thirst, frequent urination, or weight loss return in a previously stable dog.
Some veterinarians also offer at-home glucose monitoring using portable meters or continuous glucose monitors that attach to the skin. At-home readings can be more accurate reflections of your dog’s normal state, since the stress of a vet visit can temporarily raise blood sugar.
Fructosamine: The Bigger Picture
A single blood sugar reading is just a snapshot. To understand how well your dog’s diabetes has been controlled over the previous two to three weeks, your vet can run a fructosamine test. This blood test measures a protein that accumulates when blood sugar has been elevated, giving a broader view than any single glucose reading can.
For diabetic dogs, the general interpretation is straightforward. A fructosamine level of 300 to 400 µmol/L indicates good glycemic control. Levels between 400 and 450 µmol/L suggest fair control, meaning adjustments might help. Anything above 450 µmol/L points to poor control and usually prompts a change in insulin dose, timing, or diet. Fructosamine is especially useful when glucose curves are inconsistent or when you suspect your dog’s diabetes management isn’t working as well as daily readings suggest.
When Blood Sugar Swings Too Far
One of the trickiest problems in canine diabetes management is the Somogyi effect, a rebound pattern where blood sugar drops too low and then shoots too high. It happens when the insulin dose is actually too strong. The body detects the dangerous low and dumps stored sugar into the bloodstream as an emergency response, causing a dramatic spike. The pattern looks like blood sugar falling below about 80 mg/dL (often well below) followed by a rebound above 300 mg/dL.
The danger is that a vet seeing only the high rebound number might increase the insulin dose, making the problem worse. This is one reason glucose curves, rather than single spot-checks, are so important. If your dog’s blood sugar seems to swing wildly between very low and very high, the Somogyi effect is a likely explanation, and the solution is typically reducing the insulin dose rather than raising it.
What Affects Daily Readings
Blood sugar in a diabetic dog doesn’t stay at one number. It rises after meals and drops after insulin injections, creating a predictable wave pattern through the day. The timing and composition of meals matter. Most vets recommend feeding your dog at consistent times, ideally right before or alongside insulin injections, so the post-meal glucose rise and the insulin’s peak activity overlap.
Exercise also lowers blood sugar, sometimes unpredictably. A long walk or vigorous play session can cause a sharper drop than usual, especially if it happens near the time insulin is peaking. Keeping exercise routines consistent from day to day helps prevent unexpected lows. Illness, stress, and other medications can push blood sugar higher, which is why a dog that was previously well controlled can suddenly show elevated readings during an infection or after starting a new treatment for an unrelated condition.
Signs Your Dog’s Levels Are Off
Even with regular testing, it helps to know what uncontrolled blood sugar looks like in daily life. When blood sugar is too high for extended periods, you’ll notice increased thirst, frequent urination, weight loss despite a normal appetite, and lethargy. These are the same symptoms that likely led to the diabetes diagnosis in the first place, and their return signals that the current treatment plan isn’t keeping glucose in range.
Low blood sugar is less common but more immediately dangerous. Early signs include restlessness, trembling, and disorientation. As it worsens, dogs may become wobbly, unresponsive, or experience seizures. If you see these signs, offering a small amount of sugar water, honey rubbed on the gums, or food (if your dog can swallow safely) can help while you contact your vet. Repeated episodes of low blood sugar usually mean the insulin dose needs to come down.