Continuous glucose monitoring (CGM) is commonly used to assess the quality of control in human diabetics on insulin treatment. Devices such as the “Freestyle Libre 2” (Abbott Laboratories Ltd) are also now widely used to assist in monitoring the quality of control of diabetic dogs and cats. Such devices measure glucose levels in tissue (interstitial) fluid rather than in capillary or venous blood. This form of monitoring can be useful during the induction phase to establish how insulin is working over a period of days. In cases where clinical signs persist despite therapy, this approach can better inform actions to improve clinical response.

CGM has the advantage of producing a continuous glucose curve while the device remains in situ. Results are displayed and recorded on the pet owner’s mobile phone so that they can be readily shared with the clinic. Some pitfalls in interpretation remain and it is important to recognise that the levels of glucose found in tissue fluid may not exactly match those seen with blood glucose monitoring.

However, this technology offers a less invasive and more convenient way to understand how administered insulin is impacting glucose levels in the pet’ body. In conclusion, this technique suits many diabetic pet patients, and complements and reduces the need for multiple measurements of blood glucose, improving both value for money and clinical decision-making.

The Glucose Curve

Blood glucose curves (BGCs) are useful during the initial stabilisation of a diabetic dog and when clinical signs suggest there is poor control of blood glucose levels. They are not as useful when the history of clinical signs, physical examination and body weight and body condition score suggest good diabetic control.

A BGC will help to pinpoint the speed of onset of insulin following injection, the duration of action of the insulin, the effectiveness of the insulin to maintain blood glucose levels between 5.5 and 14.0 mmol/l and the approximate time of the nadir.

It is important to remember that there is a lack of consistency in the results of serial blood glucose curves (even in the same patient) which can create frustration for vets - but this is a reflection on all the variables that can affect blood glucose concentrations in dogs¹.

Try our online glucose curve generator.

The BCG may also help to differentiate between the problem of short duration of insulin activity versus the Somogyi effect, although this needs careful interpretation.

How to complete a glucose curve

The dog should be fed and then injected with Caninsulin^® (porcine insulin zinc suspension) as per the home schedule. This may be done by the owner, and verified by a vet, or by a member of the veterinary team. If the dog exercises at home during the day, the same exercise routine should be adhered to while the dog is in the clinic.

Blood sampling:

 

Interpreting a glucose curve

For insulin effectiveness:

Glucose nadir goal:

 

Measuring blood glucose

Two methods of taking blood samples to produce glucose curves include:

 

Whichever method of sampling is used, ensure it is consistent throughout the test. After the animal has been stabilised successfully, routine rechecks should be carried out around every 2–4 months.

Careful monitoring and control during maintenance will help to limit the long-term complications associated with diabetes.

Blood glucose concentrations

The aim of therapy is not to produce a series of blood glucose concentrations that are within the reference range but to produce a blood glucose curve that approaches the reference range, avoiding potentially fatal hypoglycaemia. An example of a stable dog with diabetes is a blood glucose range of 5.5–14.0 mmol/l for most of a 24-hour period, spending the majority of time (>75%) below the renal blood glucose concentration threshold for tubular glucose resorption, which is 10-12 mmol/l.

Ideal blood glucose curve

Below is an example of an ideal blood glucose curve for a dog on once-daily dosing where the range remains between 5.5 -14.0 mmol/l for most of the test period. Please note that for a dog on twice-daily dosing the curve will appear very similar, but just within a 12-hour time period. Newly diagnosed dogs may not present an ideal BGC at first, but with proper maintenance, the curve will become closer to the ideal.

Blood glucose measured in mmol/l

Punctual blood samples in dogs

Monitoring with blood samples

The term serial blood sample applies when a limited number of blood samples are taken at specific intervals during the day. A regular glucose curve requires blood sampling at least every 2 hours for a minimum of 12 hours (for patients on twice daily injections).

Serial blood sample timing

The first blood sample should be taken early in the morning prior to the first meal and insulin injection. Several samples should then be taken around the expected time of the nadir – this may be approximately 7.5 hours later. If the dog receives insulin injections twice a day, blood sampling should be done before each meal.

If slight hypoglycaemia or hyperglycaemia is detected, but all other parameters (i.e. urine, appetite, water uptake, weight and general body condition) suggest improvement and stability, the insulin dose is likely to be correct as is. If there is any uncertainty, or a dose change is possibly indicated, a regular blood glucose curve can be performed.

Precaution

It can be impossible to differentiate a Somogyi overswing from rapid metabolism or resistance to insulin with only a few blood samples.

Glucose Blood Sampling

A glucometer or glucose test strips are needed to test the blood. Check instructions from the glucometer or test strips. Blood can be collected easily from the patient’s pinna. Alternative sites could be considered, including the tail, inside the lip, elbow callous and foot pads, depending on preference and the dog's comfort level.

Step 1

Make sure that the dog's ear / alternative collection site is warm for easier collection. Warm between palms if needed.

Step 2

Quickly prick a clean, hairless part of the skin with a sterile lancet or hypodermic needle.

Step 3

Collect the blood droplet onto the glucose test strip as per instructions provided.

Step 4

Gently but firmly press clean cotton or gauze onto the collection site until it stops bleeding.

Step 5

Read the test strip or insert the sample into the glucometer as instructed. Compare the reading to the normal level in dogs.

If blood samples are taken at home, you should advise your owner to keep records of the readings to share with you.

Please note that blood glucose measurements assessed via hand-held glucometers can vary much as 15% from samples sent to the laboratory. If a reading seems unusual or does not match the clinical signs, a second reading should be taken, or another method used to confirm the blood glucose concentration.

Evaluation of glycosuria, ketonuria, and monitoring

Urine only tests positive for glucose if the blood glucose concentration remains above the renal threshold for a substantial period. This occurs when glycaemia reaches 10–12 mmol/L in the dog.

If used in conjunction with a series of blood samples taken around the time of the expected nadir and evaluation of clinical signs, urine sampling can be a valuable monitoring tool. However, when adjustment of insulin dose is necessary, the preferred method of monitoring is by evaluation of glycaemia by performing a glucose curve. Urine monitoring is also a quick and easy method of detecting ketones (ketonuria) and hence a potential emergency—see diabetic ketoacidosis.

Client urine testing protocol:

It is often not practical to expect dog owners to take a series of urine samples throughout the day at specific times. There may be occasions where monitoring of urine glucose and ketonuria is a useful additional monitoring tool, however changes to the insulin dose should never be based on urine testing alone. Either persistent glycosuria or ketonuria will indicate the necessity of a re-evaluation and glucose curve.

Fructosamine and glycosylated haemoglobin

Fructosamine and glycosylated haemoglobin (GHb) are 2 glycated proteins commonly used for monitoring human patients. These 2 proteins are markers of mean glucose concentration and their amount is proportional to the blood glucose concentration. The concentration of these proteins is not affected by stress; therefore, they are ideal for monitoring dogs with diabetes, especially those prone to stress in the veterinary clinic².

Although fructosamine and GHb are good tools for determining stabilisation, they will not identify an underlying problem, nor will they replace glucose curves conducted for adjustments of therapy. Rather, they give an idea of the control of the glycaemia for a long period: fructosamine reflects the glycaemic control for the previous 1 to 3 weeks and GHb for the prior 2 to 4 months.

Fructosamine is preferred over GHb to assess glycaemic control. It is more commonly evaluated than GHb because more analytical assays are available that are less time- consuming and uncomplicated.

Fructosamine

Most animals with diabetes will not always have optimal control of blood glucose, thus fructosamine concentrations are unlikely to lie entirely within the reference range for normal dogs. Single fructosamine measurements should be interpreted in the light of clinical signs of diabetes, body weight, and blood glucose concentration. In general, the closer the fructosamine concentration is to the reference range for healthy dogs, the better the glycaemic control.

Fructosamine reference ranges³                                 Fructosamine values

Dogs                                                                                   (mmol/L)  

Normal dog without diabetes                                              225–365

Newly diagnosed dog                                                         320–850

Treated dogs with diabetes:

Excellent control                                                                 350–400

Good control                                                                       400–450

Fair control                                                                          450–500

Poor control                                                                         >500

Advantages of measuring fructosamine

Limitations of fructosamine measurements

Glycosylated haemoglobin (GHb)

GHb is produced by the non-enzymatic, irreversible binding of glucose to haemoglobin in erythrocytes. The glycosylation of haemoglobin is a gradual process and is not affected by acute or transient hyperglycaemia.

Glycosylated (glycated) haemoglobin concentration can be used as a screening test for diabetes mellitus, as well as for the monitoring of glycaemic control in treated animals.

Advantages of GHb measurements

 

Limitations of GHb measurements

 

Test results and interpretation vary greatly depending on the literature consulted and the laboratory where the test is performed. Therefore, it is recommended to ask each laboratory for the guidelines for the purposes of interpretation.

Insulin Resistance

From stress, infections and obesity

Stress or infections (urinary tract infections, pyoderma) can lead to a decline in the sensitivity of target tissues to insulin. Obese animals have reduced insulin sensitivity.

From other hormones

Endogenous or exogenous hormones may reduce the effects of insulin. When treating an animal for diabetes mellitus, medication with progestogens should be discontinued immediately. Entire bitches should be spayed.

If animals are being treated with exogenous corticosteroids, alternatives to this treatment should be sought. If this is not feasible, efforts should be made to minimise the corticosteroid dose, whilst ensuring the daily dose remains consistent. It would be preferable to have a very low daily dose than move to alternate day therapy, as this will lead to changes in the insulin requirement and potential instability.

Cushing’s disease (hyperadrenocorticism) leads to an increase in the endogenous production of corticosteroids and has many clinical signs in common with diabetes. Where dogs are not responding as expected to their insulin dose, an ACTH stimulation or low dose dexamethasone test should be performed to rule out or help diagnose this condition. Management should be conducted with care, as a reduction in endogenous corticosteroids may reduce the insulin dose required and potentially lead to hypoglycaemia.

Blood glucose curve

See the following graph for an example of a blood glucose curve in a case of insulin resistance. Insulin was injected at time=0 hours.

For this case, the cause of insulin resistance must be diagnosed and managed

Blood glucose measured in mmol/L

Rapid metabolism of insulin

The duration of action of insulin is less than desired (10–12 hours for twice-daily administration; 20 hours for once-daily administration).

Blood glucose curve

See the following graph for an example of blood glucose in a case of rapid metabolism of insulin.

To solve this issue, increase insulin dosing from once to twice daily.

Blood glucose measured in mmol/L

Dietary Control^4,5,6

Since almost all dogs with diabetes have insulin-dependent diabetes mellitus (IDDM), dietary management will not remove the requirement for insulin. Any adjustments in diet and feeding practices should be directed at correcting or preventing obesity, maintaining consistency in the timing and caloric content of the meals and ideally minimise the postprandial increase in blood glucose concentration.

However, key to all of these efforts is that the diet is palatable to the dog. The best diet for the dog needs to be one that it will readily eat in the first instance.

The essential features of the diet should be:

 

There are a number of prescription diets that have been specially formulated for the management of diabetes.

These can be particularly useful for achieving weight loss in obese patients. However, most dogs with diabetes can be stabilised on a carefully controlled program using their normal diet. 

Clean drinking water should always be available. A reduction in excessive water consumption indicates successful management of diabetes mellitus.

Importance of an ideal body weight

In dogs that are underweight or overweight, it is desirable that the ideal body weight is reached by gradual weight gain or loss, respectively.

In underweight animals, very calorie dense diets should be avoided, especially those that are high in soluble carbohydrates.

Obesity contributes to insulin resistance. Overweight dogs should lose weight in a gradual, controlled fashion. Weight loss in obese animals decreases the insulin requirement. Diets designed to promote weight loss are high-fibre diets and are suitable for feeding to dogs with diabetes.

For specific information about dietary control, see Tailoring Diets for Healthy Dogs.

Combating an incorrect insulin dose

An insulin dose that is too high may bring about the Somogyi effect or rebound hyperglycaemia. This is produced because blood glucose concentrations fall too rapidly. The moment that the Somogyi effect is triggered is very individual—it is a life-saving response.

The body attempts to counteract the decline in the blood glucose concentration through a chain of reactions:

 

If the morning polyuria is thought to be the result of an insufficient insulin dose and a higher dose is given, the problem will be aggravated. An even more pronounced Somogyi effect will follow. Eventually the counter-regulatory mechanisms may become exhausted resulting in severe hypoglycaemia.

Hyperglycaemia caused by a Somogyi effect can sometimes persist for as long as 3 days after a single hypoglycaemic episode. As a result, blood glucose concentrations do not always normalise within a few days after lowering the insulin dose.

It is worth considering a Somogyi overswing if a number of these parameters are present:

 

Please note: these parameters should not be considered as indicators of a Somogyi overswing on their own. Persistent morning glucosuria can be present in many diabetic patients because blood glucose concentrations will often rise above the renal threshold by morning – especially in dogs stabilised on once-daily insulin injections.

Further diagnostic is required in dogs showing clinical signs, alongside the parameters indicated above.

Diagnosing Somogyi effect

A blood glucose curve can help detect a Somogyi effect and confirm that a dog's insulin dose needs to be reduced.

Any of the following blood glucose curves can be suggestive of the Somogyi effect:

 

Blood glucose curve indicating Somogyi effect

The following graph is an example of a blood glucose curve in a case of rebound hyperglycaemia. The graph is based on canine once-daily dosing and should be used as a guideline only. Insulin was injected at time=0 hours.

The solution to this is to decrease the insulin dose by 50% or return to the starting dose, whichever is lower.

Hyperglycaemia because of a Somogyi effect can persist for as long as 3 days after a single hypoglycaemic episode. As a result, blood glucose concentrations do not always stabilise within the first few days after lowering the insulin dose.