What Is Dangerously High Blood Sugar for a Cat?

Blood sugar, or blood glucose, is normally strictly controlled by your cat’s body. But when this control mechanism breaks down, blood sugar can run dangerously high. This is called hyperglycemia. If left unchecked, hyperglycemia in cats can develop into a life-threatening condition called diabetic ketoacidosis (DKA).

The most common cause of high blood sugar in cats is diabetes. Diabetes treatment for cats typically includes daily medication, such as Bexacat or insulin, as well as properly timed feedings and regular exercise. 

In this article, we’ll cover what high blood sugar is, and what your veterinarian will do if they suspect your cat has high blood sugar. 

What Is High Blood Sugar in Cats?

Your cat’s body runs on glucose, just like the human body. The glucose level in the blood is tightly controlled by feedback mechanisms. This is called glucose homeostasis.

When glucose is absorbed from the gut after eating, an organ called the pancreas recognizes the higher glucose levels and produces insulin. This hormone moves extra glucose into cells where it can be used or stored, keeping the glucose in the blood at safe levels. When blood glucose gets low, the pancreas releases a different hormone called glucagon that tells the liver to release glucose again. This raises the level in the blood back to normal. 

If this control mechanism breaks down, cats can have high blood sugar for a long period of time. The most common reason for this to happen is diabetes. Cats get type 2 diabetes, meaning their pancreas produces insulin but their cells don’t respond normally to it. This causes them to have high glucose in the blood, but because the cells aren’t responding, they are unable to get the glucose into the cells to be used as energy. 

What Is Dangerously High Blood Sugar for a Cat?

A cat’s normal blood glucose is 60–160 mg/dL. With stress, this might rise above normal, but it should drop down again within an hour or two. Sustained levels of over 160 mg/dL are abnormal and should be investigated. 

However, diabetic cats often have a blood sugar of over 400 mg/dL. This is a dangerously high blood sugar for a cat. With this much glucose in the blood, the pancreas will be getting exhausted from trying to produce insulin to counteract the hyperglycemia. In addition, the cells of the body will be starting to starve, as they won’t be getting enough glucose. 

The body recognizes the cells are struggling and starts to break down fat for energy instead. This causes chemicals called ketones to build up in the body, which can lead to serious, life-threatening illness.

Causes of High Blood Sugar in Cats

The most common cause of persistent high blood sugar in cats is diabetes mellitus, usually just called diabetes. Diabetes in cats is fairly common, affecting approximately 1 in 200 cats, particularly males and cats of specific breeds, like Norwegian Forest Cats and Burmese (1).

Temporary, mild rises in blood sugar can be seen at times of acute stress, such as during a vet visit. This is called stress hyperglycemia and is why vets will never assume a cat has diabetes from a single high blood glucose reading. Instead, they will check urine samples and other blood values to prove the blood sugar is staying high.

Symptoms of High Blood Sugar in Cats

In cats who get a mild blood sugar rise when visiting the vet, you’re unlikely to see any symptoms. But cats with long-term high blood sugar levels caused by diabetes experience symptoms such as drinking more and urinating more. You might also notice:

• Weight loss 
• Appetite changes (excessive hunger or no interest in food)
• Blood in the urine (caused by urinary infection)
• Changes in normal grooming, leading to an untidy coat

When blood sugar gets dangerously high and diabetic ketoacidosis develops, you might also see:

• Vomiting
• Lethargy, weakness, or low energy
• Collapse

If you suspect your cat has high blood sugar, you should take them to a veterinarian. If you suspect there could be dangerously high blood sugar, you should contact the nearest open veterinarian as an emergency.

Diagnosing High Blood Sugar in Cats

Hyperglycemia is usually diagnosed with a blood test. Only a tiny amount of blood is needed. The veterinarian may just prick your cat’s paw and collect the blood on a small strip of paper, which is read by a machine. However, a diagnosis of hyperglycemia doesn’t mean much on its own, and the underlying cause will need to be found. 

A physical exam will give clues, but the main results come from blood and urine tests. Alongside the blood glucose test, a fructosamine blood test can help to differentiate transient, stress-induced hyperglycemia from a more severe hyperglycemia caused by diabetes.

Urine tests can also show the presence of glucose, which again points to diabetes rather than a mild and acute high blood sugar caused by stress. Your vet will also check for evidence of a secondary urine infection, which is common in cats with diabetes.

How to Treat High Blood Sugar in Cats

If your cat is diagnosed with high blood sugar, treatment is essential. Without treatment, the blood sugar will continue to rise to dangerously high levels, and they will get diabetic ketoacidosis (DKA). This is an emergency, as DKA can quickly become fatal. Prompt treatment not only avoids this potential, but it also increases the chance of a cat going into diabetic remission. Remission means their diabetes goes away and they no longer need treatment. With treatment, about 1 in 3 diabetic cats go into remission (2), according to a recent paper. However, some cats then relapse.

There are two main treatment options for high blood sugar in cats: insulin injections and insulin alternatives.

Insulin Alternatives for Cats with High Blood Sugar

There are now needle-free alternatives to insulin, such as Bexacat (bexagliflozin tablets), that are given orally. Bexacat blocks the kidneys from reabsorbing glucose, meaning extra glucose from the blood exits the body in the urine. Since this tablet is given only once a day, and the dosing is simple, it’s generally easier for pet parents to manage than insulin injections. It’s also slightly less intensive, monitoring-wise. However, Bexacat can’t be used in cats who have already started treatment on insulin — it’s only suitable for new cases of high blood sugar in otherwise healthy cats.

Insulin Injections for Cats with High Blood Sugar

Cats taking insulin require regular injections, either once or twice daily, depending on the product and individual cat response. Although most cats tolerate these regular injections, it can still be difficult for some pet parents to manage. Insulin treatment can also be risky (overdose and underdose are both dangerous), which means intensive monitoring may be needed to find the correct dose. This also makes insulin treatment expensive.

Diets for Cats with High Blood Sugar

Prescription diets can help with high blood sugar in cats. These high-fiber diets help to prevent a blood sugar spike after eating. This helps the body regulate blood glucose levels. While prescription diets may be helpful, they generally can’t be used alone. One study found that more cats achieved remission if fed a low-carbohydrate wet diet than a prescription diabetes diet (2). It’s best to discuss diabetes diets with your veterinarian before making any changes.

General Cost of Treating High Blood Sugar in Cats 

Diabetes can be expensive to treat. In addition to medication costs, cats with diabetes generally need repeated blood sugar checks and visits to the veterinarian. Generally, costs are highest in the first couple of weeks, during diagnosis and when cats need more regular checks. That said, high blood sugar can still be expensive to treat.

In general, you can expect high blood sugar in cats to cost $500-$1,000 in the first month of diagnosis, and then usually around $150-$300 per month thereafter.

How to Prevent High Blood Sugar in Cats

Obese cats are more likely to get diabetes. Maintaining a healthy body weight, and treating cats as soon as possible if they gain weight, is key to preventing high blood sugar in cats. In cats of a normal weight, there is some suggestion that a predominantly dry diet may increase the risk of high blood sugar developing (3). However, the link isn’t clear, so preventing high blood sugar is not a reason to change your cat’s diet if they’re doing well on it. It’s far more important to make sure your cat gets plenty of water and exercise.

Summary

Persistently high blood sugar in cats (also called hyperglycemia) is not normal and should be investigated. The most common cause is diabetes. If left untreated, cats can develop diabetic ketoacidosis, a severe and life-threatening condition. There are several ways to treat feline hyperglycemia. If you suspect your cat might have high blood glucose, talk to your veterinarian.

Related Conditions 

• Diabetic Ketoacidosis
• Obesity
• Diabetes 

References

1. O’Neill, D G et al. “Epidemiology of Diabetes Mellitus among 193,435 Cats Attending Primary-Care Veterinary Practices in England.” Journal of veterinary internal medicine vol. 30,4 (2016): 964-72. doi:10.1111/jvim.14365
2. Rothlin-Zachrisson, Ninni et al. “Survival, remission, and quality of life in diabetic cats.” Journal of veterinary internal medicine vol. 37,1 (2023): 58-69. doi:10.1111/jvim.16625
3. Öhlund, M et al. “Environmental Risk Factors for Diabetes Mellitus in Cats.” Journal of veterinary internal medicine vol. 31,1 (2017): 29-35. doi:10.1111/jvim.14618