Feline Diabetes Mellitus: Diagnosis, Insulin Therapy, and the Path to Remission

Why cats get diabetes and dogs don't (the same way)

Cat beta cells are unusually vulnerable to amyloid deposition -- a process where the protein IAPP (islet amyloid polypeptide) misfolds and accumulates in the islets of Langerhans, progressively replacing functional beta cells with insoluble plaques. Obesity drives insulin resistance, which drives beta cells to work harder, which increases IAPP production and accelerates amyloid deposition. High-carbohydrate diets compound the problem by forcing chronically elevated glucose, which directly damages beta cells through glucotoxicity. Cats fed high-carbohydrate dry kibble their entire lives have substantially higher diabetes risk than cats on low-carbohydrate wet diets -- a finding supported by multiple epidemiological studies and relevant to prevention as well as treatment.

Recognizing feline diabetes: the four Ps

The classic presentation is the "four Ps": polyuria (large urine volume, often overwhelming the litter box), polydipsia (drinking from faucets or unusual water sources), polyphagia (ravenous appetite), and weight loss despite eating well. The combination of a hungry cat losing weight is almost pathognomonic in middle-aged to older, overweight male cats (males are 1.5 times more likely than females). A plantigrade stance -- walking flat on the hocks rather than on the toes -- indicates diabetic neuropathy and signals advanced or poorly controlled disease. Some cats present in diabetic ketoacidosis (DKA) with vomiting, lethargy, and a fruity breath odor; this is a medical emergency requiring hospitalization.

Diagnosis

Diagnosis requires persistently elevated blood glucose (above 250 to 300 mg/dL on multiple measurements) plus glucosuria (glucose in the urine). The challenge: cats stress-hyperglycemia -- a single blood glucose reading above normal in a stressed clinic cat can exceed 300 mg/dL in a non-diabetic animal. Fructosamine (a measure of average glucose over the preceding 2 to 3 weeks) distinguishes chronic hyperglycemia from acute stress hyperglycemia; fructosamine above 350 to 400 micromol/L confirms persistent hyperglycemia. In difficult cases, continuous glucose monitoring (CGM) devices designed for humans (Freestyle Libre) can be attached to a shaved patch of skin and provide 2-week glucose curves without the stress of clinic visits.

Treatment: the protocol that maximizes remission chance

Insulin: Long-acting insulin analogs -- glargine (Lantus) or detemir (Levemir) -- produce the highest remission rates in cats (40 to 60% for glargine in early cases vs. 20 to 30% for intermediate-acting insulins like PZI). Starting dose is typically 1 to 2 units per cat twice daily subcutaneously, adjusted based on glucose curves. The goal of initial therapy is not tight glucose control but avoiding hypoglycemia while eliminating glucotoxicity; glucose curves are performed weekly initially.

Diet: Switching to a low-carbohydrate (less than 10% metabolizable energy from carbohydrates) wet diet is as important as insulin. High-protein, low-carb wet foods eliminate the postprandial glucose spikes that drive pancreatic exhaustion. Prescription diabetic diets (Hill's m/d, Purina DM) are formulated for this purpose; many over-the-counter grain-free wet foods achieve similar carbohydrate levels. Dry food is nearly impossible to formulate to less than 25 to 35% carbohydrates and should be eliminated.

Monitoring: Home glucose monitoring -- using a glucometer calibrated for cats (AlphaTrak 2) or a human glucometer with a cat-specific adjustment -- allows owners to perform glucose curves without the stress of clinic visits. Glucose should remain between 80 and 300 mg/dL during early treatment. A glucose below 50 mg/dL requires immediate insulin dose reduction and often emergency feeding; below 40 mg/dL is a hypoglycemic crisis requiring oral glucose (corn syrup on the gums) and immediate veterinary contact.

Signs of remission and what to do

Remission occurs when blood glucose normalizes without insulin for a minimum of 4 consecutive weeks. Signs preceding remission: glucose curves that stay below 200 mg/dL throughout the day, decreasing insulin requirements, cat becoming more active and regaining weight appropriately. When a diabetic cat starts having hypoglycemic episodes on the same dose that previously produced normal readings, reduce the dose immediately -- the beta cells are recovering. Approximately 30% of cats in remission relapse within 6 months; maintaining a low-carbohydrate diet and body weight in the healthy range dramatically reduces relapse risk.