A healthy dog’s fasting blood sugar falls between 75 and 120 mg/dL. Below 60 mg/dL, a dog is in clinical hypoglycemia and at risk of seizures, coma, and brain damage. Above 200 mg/dL, sugar spills into the urine and begins causing organ stress. Both extremes are dangerous, but they look very different and require different responses.
The Low End: Below 60 mg/dL
Clinical hypoglycemia in dogs is defined as a blood glucose reading below 60 mg/dL (3.3 mmol/L) accompanied by visible symptoms. The brain depends almost entirely on glucose for fuel, so when levels drop this low, neurological signs appear fast. Early warning signs include unusual lethargy, sleeping far more than normal, and reluctance to move or play. As glucose continues to fall, dogs develop tremors, lose coordination, become disoriented, and may stumble or walk as though drunk.
If blood sugar drops further without intervention, seizures and collapse can follow. A dog that becomes unresponsive or comatose from low blood sugar is in a life-threatening emergency. The longer the brain goes without adequate glucose, the greater the risk of permanent neurological damage.
Low blood sugar is most common in diabetic dogs receiving insulin, but it also affects puppies (especially toy breeds), dogs with liver disease, and dogs that have gone without food for an extended period. In a diabetic dog, an accidental double dose of insulin, a missed meal, or unusually heavy exercise can all trigger a dangerous drop.
What to Do During a Low Blood Sugar Emergency
If your dog shows signs of hypoglycemia, rub corn syrup, honey, or glucose paste directly onto the gums. This works even if the dog is unconscious, because sugar absorbs through the oral tissues without swallowing. If you don’t have any of those on hand, dissolve regular table sugar in a small amount of water and apply it to the gums the same way. The goal is to get glucose into the bloodstream as quickly as possible while you arrange transport to a veterinarian.
If your dog is diabetic or has a history of low blood sugar episodes, keep corn syrup or glucose paste somewhere accessible at all times. These episodes can escalate within minutes, and having a sugar source ready can be the difference between a scare and a crisis.
The High End: Above 200 mg/dL
A dog’s kidneys can reabsorb glucose from the blood and return it to the body, but only up to about 200 mg/dL. Once blood sugar exceeds that threshold, glucose spills into the urine. This is the point where you’ll notice the classic signs of uncontrolled diabetes: excessive thirst, frequent urination, increased appetite despite weight loss, and gradual muscle wasting. A dog whose blood sugar consistently sits above 200 mg/dL is not in immediate crisis, but the condition is actively damaging the body.
Sustained high blood sugar causes dehydration (because the kidneys pull extra water to flush out the excess glucose), weakens the immune system, and can lead to cataracts and nerve damage over time. The longer blood sugar stays elevated, the more cumulative harm it does.
When High Blood Sugar Becomes an Emergency
The most dangerous complication of prolonged, severely elevated blood sugar is diabetic ketoacidosis, or DKA. This happens when a dog’s body, unable to use glucose properly, starts breaking down fat for energy at an unsustainable rate. The byproducts of that fat breakdown (ketones) build up in the blood and make it dangerously acidic.
DKA symptoms go well beyond the typical signs of diabetes. A dog in DKA will be visibly weak and lethargic, refuse food, vomit repeatedly, and become noticeably dehydrated. You may notice a sweet or fruity smell on the dog’s breath. DKA is fatal without veterinary treatment, and it can develop over just a day or two in a dog whose diabetes is unmanaged or whose insulin dose has become inadequate.
Blood sugar readings in DKA are often well above 300 mg/dL, sometimes exceeding 500 or 600 mg/dL. But the number alone doesn’t tell the full story. A dog at 350 mg/dL who is eating, drinking, and acting normally is in a very different situation than a dog at 350 mg/dL who is vomiting and refusing food. The behavioral signs matter as much as the reading.
Target Range for Diabetic Dogs
If your dog is diabetic and on insulin, the treatment goal isn’t to bring blood sugar back to the normal 75 to 120 mg/dL range of a healthy dog. That aggressive a target increases the risk of dangerous lows. Instead, veterinary guidelines from the American Animal Hospital Association recommend keeping blood glucose below 200 mg/dL (the kidney spillover point) while avoiding hypoglycemia. A well-managed diabetic dog will spend most of the day somewhere between 100 and 200 mg/dL, with occasional spikes after meals.
If blood sugar dips below 60 mg/dL during treatment, insulin is typically paused until glucose climbs back above 180 mg/dL. Dose adjustments are made gradually, usually 10 to 25 percent at a time, to avoid overcorrection. Successful management shows up less in perfect numbers and more in how your dog looks and feels: steady weight, normal thirst and urination, good energy, and no episodes of weakness or collapse.
Signs That Warrant Immediate Action
Not every owner has a glucose meter at home, so knowing what to watch for matters more than knowing exact numbers. On the low side, watch for sudden lethargy, trembling, unsteadiness, glassy eyes, or unresponsiveness. These signs can develop quickly and escalate within minutes. Apply sugar to the gums and get to a vet.
On the high side, the red flags are vomiting, complete loss of appetite, extreme weakness, heavy panting, and a sweet or chemical odor on the breath. These suggest DKA or another acute complication and require emergency veterinary care. The more typical signs of high blood sugar (increased thirst, frequent urination, weight loss despite a good appetite) develop gradually and point to uncontrolled diabetes that needs treatment but isn’t yet a same-day emergency.