A tech's guide to the medical management of DM in cats and dogs
By David Liss, BA, RVT, VTS (ECC, SAIM), CVPM
HALIFAX – Diabetes mellitus (DM) is a relatively common chronic endocrinopathy in dogs and cats. Patients can be stable or emergent and will require long-term management. As the veterinary technician is an integral part of this management, they should understand the underlying pathophysiology and treatment recommendations.
The role of insulin in DM
Diabetes mellitus can be an absolute or relative lack of insulin. Insulin is a hormone synthesized in the β-cells of the Islets of Langerhans in the pancreas. It is released in response to increased blood glucose concentrations. An absolute lack of insulin is termed insulin-dependent diabetes mellitus (IDDM) and typically results from β-cell failure. Relative lack of insulin is often referred to as non-insulin dependent diabetes mellitus (NIDDM), and results from possible low or normal insulin synthesis but inappropriate cellular interactions resulting from insulin resistance. The resulting hyperglycemia is concurrently toxic to β-islet cells, resulting in further pancreatic damage and eventually possibly leading to sudden and severe IDDM.
Canine diabetes mellitus can be aligned with Type I DM (insulin-dependent) in humans and results in an absolute lack of insulin. β-cells in the Islets of Langerhans no longer produce insulin and therefore serum concentrations go to zero. Feline diabetes tends to align itself with Type II or NIDDM. Canine diabetes is typically permanent, while approximately 15-70% of cats may experience remission.
History, clinical signs, diagnosis
History and clinical signs of diabetes mellitus include polyuria, polydipsia, polyphagia, and weight loss. A dog or cat presenting with these clinical signs will require further documentation of hyperglycemia and concurrent glucosuria to support a diagnosis of DM. Cats should have repeat measurements for blood glucose and urinalysis to establish prolonged and consistent hyperglycemia/glucosuria.
Treatment
Insulin therapy and nutrition are the two major modalities of treatment that currently exist.
Insulin therapy
The chart below summarize the various types of insulin:
Duration of action |
Generic name |
Trade name (s) |
Pharmacokinetics |
Use |
Dogs/Cats/Both? |
Maintenance? |
Short acting |
Regular insulin |
Novolin-R, Humulin-R |
Onset: Immediate |
Emergency situations |
Both |
N |
Moderate (intermediate) acting |
Neutral Protamine Hagedorn (NPH) |
Humulin-N, Novolin-N |
Onset: 0.5-2 hours |
Common in dogs |
Dogs mainly |
Y |
|
Porcine Lente insulin |
Vetsulin |
Average length = 8 hours |
Common in dogs and cats |
Both |
Y |
Long-acting |
Protamine Zinc Insulin |
ProZinc |
Onset: 1-4 hours |
Common in dogs and cats |
Both |
Y |
|
Insulin Glargine |
Lantus |
Onset: 2 hours |
Common in cats |
Cats |
Y |
|
Insulin Detemir |
Levemir |
Onset: 2 hours |
Rarely used- dogs only |
Dogs |
Y |
Dietary therapy
Weight loss is very important in the diabetic patient with some cats achieving remission after weight loss. Dogs tend to require a higher carbohydrate load than cats so their diet should consist of complex carbohydrates and fibre to promote satiety and control the glucose release from the gut. Consistent feeding schedules are very important to maintain regular infusions of carbohydrates and subsequent insulin actions. Feeding should be twice a day in patients receiving once-daily insulin and ideally four times a day in patients receiving twice-daily insulin.
Monitoring
A blood glucose curve measures serum glucose concentrations over a fixed amount of time, ideally 24 hours but usually around 12 hours. During this time blood glucose samples are taken at 1-2 hour intervals in dogs and cats, and every 4 hours in cats on glargine, and recorded. The samples will determine the glucose nadir, or the lowest blood glucose reading that is obtained. The actual reading and how many hours post injection should be recorded.
Monitoring will also determine the insulin’s duration of effect, calculated as the time from insulin injection until the blood glucose drops, and then exceeds 220-250 mg/dL.
It will also determine if the insulin actually lowers the blood glucose, and whether it has any effect.
Blood glucose curves should be done one week after treatment is initiated or changed (new insulin type); whenever changing an insulin dose is required; whenever hypoglycemia is suspected; and any time a change in clinical history is observed.
Venous and capillary samples are accurate but testing methodology (in-house analyzer or portable unit) and site (ear, cephalic vein, etc.) should be consistent throughout the curve.
Blood glucose curve results give information about the duration of effect, nadir, and confirm whether the insulin dose is appropriate. The chart below gives a guideline as to how to interpret blood glucose curves:
Dogs
Pre-insulin BG |
Nadir |
Action taken |
>360 mg/dL |
>180 mg/dL |
Increase insulin by 25% |
< 180 mg/dL |
<54 mg/dL |
Decrease insulin by 50% |
270-360 mg/dL |
90-180 mg/dL |
No change to dose |
190-270 mg/dL |
54-90 mg/dL |
No change OR decrease- Use the nadir AND the next proinsulin dose |
Fructosamine testing measures the levels of fructosamine, a glycated protein; it captures longer-term glycemic control.
Control level |
Fructosamine level (mmol/L) |
Excellent control |
350-400 |
Good control |
400-450 |
Fair control |
450-500 |
Poor control |
>500 |
Complications and issues with DM/insulin therapy
Since DM is a complex and variable disease, there are many associated complications and issues, both with the disease itself and insulin therapy.
Insulin-induced hyperglycemia, also known as Somogyi phenomenon, results in rebound hyperglycemia causing a “falsely” high blood glucose reading that, if interpreted incorrectly, would result in an increase in insulin dosing. A diagnosis is made with blood glucose curves and is suspected when signs of hypoglycemia occur in the afternoon. In this instance, the insulin dose should be reduced by 25-50% and the blood glucose curve rechecked in one week.
If the insulin duration is less than 18 hours and clinical signs of hyperglycemia return in the evening, a rapid insulin metabolism should be suspected. Diagnosis is made with blood glucose curves, and if confirmed, owner education should be re-evaluated and compliance assessed. The dose can also be switched to twice-daily (if currently once-daily) or a longer acting insulin.
Insulin resistance is manifested by persistent hyperglycemia (>300-350 mg/dL) in the face of insulin doses >2µ/kg. Diagnosis is made with blood glucose curves or fructosamine levels, and again, client compliance should be assessed. A work-up should be recommended to screen for underlying diseases, including hyperadrenocorticism, pregnancy, acromegaly (cats), hypothyroidism (dogs), and renal failure.
Patients with hypoglycemia should be treated with IV dextrose if emergent, receive a blood glucose test, and a review of the client education.
Other non-insulin related complications include hypertension; cataracts; diabetic ketoacidosis, which should be treated as a critical emergency; and diabetic neuropathy, which can occur in cats and tends to result from glucose toxicity of nerve endings.
Summary
Managing diabetes in dogs and cars involves understanding when and how insulin is used, how and when to check blood glucose levels, the role of nutrition, and what signs and symptoms to watch for. A veterinary technician has an integral role to play in educating and supporting the client, to increase the likelihood of compliance and optimal health.
This article is based on David Liss’s presentation at the Atlantic Provinces Veterinary Conference in Halifax, NS.
David Liss is a registered veterinary technician in California, and holds a Bachelor’s in Sociology and an Associate’s Degree in Veterinary Technology. He also holds double board certifications as a veterinary technician specialist in emergency/critical care and small animal internal medicine and has diverse background in emergency and critical care nursing. In 2012 he obtained his certified veterinary practice manager (CVPM) credential as well. He has been technician manager at two different twenty-four-hour referral/specialty facilities in the Los Angeles area, has contributed to numerous veterinary texts and was awarded the Veterinary Technician Educator of the Year award by Western Veterinary Conference. David is also currently pursuing a Master’s in Biomedical Science.CVT
