Diabetes mellitus is one of the most common endocrinopathies in small animal practice and, at the same time, one of the most dependent on longitudinal follow-up. Therapeutic success is rarely decided at the first appointment: it is built over weeks, through dose adjustments, curve interpretation and, above all, the owner's adherence to home management. This text gathers the practical points that guide diagnosis, insulin selection and monitoring, with attention to the differences between dogs and cats.
Dogs and cats are different diseases
Although they share a name, canine and feline diabetes have distinct pathophysiologies, and this changes how we approach them.
In the dog, the disease usually resembles human type 1 diabetes: there is beta-cell destruction and insulin dependence essentially from diagnosis. Reversal is uncommon, and the patient tends to require insulin for life. Intact females deserve special attention, since diestrus and progesterone influence can precipitate or destabilize the condition — spaying is part of management.
In the cat, the picture is closer to type 2 diabetes, with insulin resistance linked to obesity and glucotoxicity on the beta cells. The most important clinical consequence is the possibility of diabetic remission: cats given early, tight glycemic control, combined with weight loss and an appropriate diet, may no longer need insulin. This window of opportunity underscores the importance of acting quickly in the newly diagnosed cat.
Diagnosis: persistent, not one-off, hyperglycemia
Diagnosis rests on combining compatible clinical signs — polyuria, polydipsia, polyphagia with weight loss — with documented persistent hyperglycemia and glucosuria. In the cat, extra care is needed: the stress of restraint and sampling can raise blood glucose substantially, producing transient hyperglycemia that does not reflect disease. For this reason, fructosamine is a valuable ally in the cat: because it reflects average glycemia over the previous two to three weeks, it helps distinguish stress hyperglycemia from true diabetes.
The initial workup should rule out and treat comorbidities and drivers of insulin resistance (infections, pancreatitis, hyperadrenocorticism in the dog, acromegaly in the cat), which undermine control if ignored.
Choosing the insulin
Insulin selection considers species, action profile and availability. In general, intermediate- to long-acting insulins are the backbone of treatment, usually given every 12 hours. In the cat, longer-acting formulations are often preferred for their stability and greater chance of favoring remission. The choice always goes hand in hand with dietary guidance: an appropriate carbohydrate profile in the cat and consistent, regular meals in the dog sustain the insulin effect.
One golden rule bears repeating: start conservative and adjust based on data. Hasty dose increases without a curve are a common cause of hypoglycemia and the Somogyi effect, in which rebound hyperglycemia masks an overdose.
Monitoring: glucose curve and fructosamine
Monitoring is the heart of treatment. The serial glucose curve — measurements across a dosing interval — allows assessment of the nadir (lowest value), duration of action and degree of control, guiding rational dose adjustments. Home capillary glucose monitoring with a glucometer and, increasingly, continuous glucose monitoring systems reduce hospital stress bias and offer a far truer view of the patient's day-to-day life.
Fructosamine complements the curve by providing a medium-term average of control, useful when an isolated curve is ambiguous or when stress interference is suspected. No test replaces the other: the combined reading of clinical signs, curve and fructosamine is what supports safe decisions.
The owner is part of the team
No protocol works without the owner. Correct insulin administration, proper vial storage, consistent timing, recognizing signs of hypoglycemia, and recording appetite, weight, water intake and urine output at home are decisive for the outcome. Clear guidance, repeated instructions and an open channel for questions turn the guardian into a continuous sensor of the patient's status between appointments.
Conclusion
Diabetes mellitus rewards method. Recognizing that dogs and cats are different diseases — with feline remission as an achievable goal — diagnosing with judgment, choosing insulin prudently, and monitoring with curve and fructosamine form the backbone of good control. Add a well-guided owner and an organized clinical record over time, and the diabetic patient stops being a frustrating challenge and becomes a manageable, rewarding case.
