Serial glucose assays provide the most detailed evaluation of a patient's response to insulin. Food and insulin should be
given on the usual schedule, and blood should be drawn for glucose measurement every two hours. If the glucose drops precipitously,
more frequent monitoring may be necessary to identify the nadir. For patients receiving once-daily insulin, the glucose curve
should be continued for 24 hours; for patients receiving twice-daily therapy, it is acceptable to measure glucose concentrations
over 10 to 12 hours. Checking the glucose concentration every four hours is generally sufficient in patients receiving glargine
since glargine has a slow onset of action (Figure 3).
Ideally, blood glucose concentrations should stay within the normal range, but this rarely occurs. As veterinary patients
do not suffer from the retinal, renal, and vascular complications seen in people, blood glucose concentrations do not need
to be as rigidly controlled. However, even mild persistent hyperglycemia can cause cataracts (in dogs) and peripheral neuropathy
(in cats). Hypoglycemia should be avoided, and prolonged or extreme hyperglycemia is undesirable. As a general rule, if the
lowest blood glucose concentration recorded in the clinic is < 70 mg/dl, the insulin dose should be reduced by 25%. If the
glucose concentration is more than 250 mg/dl on two or more readings, a 10% increase in insulin is appropriate. It is important
to remember that acute and severe hypoglycemia can trigger rebound hyperglycemia (the Somogyi effect), so never use a single
high glucose measurement as an indication to increase the insulin dose.
If the patient is doing clinically well, fructosamine assays can be performed in place of serial glucose measurements (Figure 4). Serum fructosamine reflects average serum glucose concentrations for the previous three weeks. If the fructosamine concentration
is elevated, a glucose curve is necessary before dose adjustments are made. It is not safe to arbitrarily increase the insulin
dose, as patients receiving too much insulin may have elevated fructosamine concentrations secondary to the Somogyi effect
(in which acute hypoglycemia results in severe and often prolonged hyperglycemia).
Figure 4: Are serum fructosamine assays sufficient to monitor glycemic control?
Patients requiring more than 2 U/kg/dose of insulin are regarded as being insulin-resistant. The most common causes of poor
glycemic control are concurrent diseases or problems with the storage or administration of the insulin (Table 2).
Table 2: A Stepwise Approach to Evaluating Patients with Insulin Resistance
Watching the client give a dose to the patient can be informative. Some people shake the bottle vigorously, causing damage
to the molecules, or inadvertently draw air into the syringe. When handling issues have been addressed, it is necessary to
look for other health problems that may affect the body's response to insulin. It is also worthwhile to make sure the patient
isn't receiving any other medications (including topical corticosteroids) that may antagonize the effect of insulin.
The impact of dietary formulation on canine diabetes appears to be modest. A recent study evaluating the effect of dietary
fiber on postprandial glycemia did not demonstrate a significant effect on blood glucose concentrations,10 although other studies have indicated improved fructosamine concentrations in diabetic dogs fed high-fiber diets.11,12 A palatable balanced diet is essential, but therapeutic diets may not provide substantial clinical advantages over commercial
dog food. It is more important for feeding schedules and food type to remain consistent. I recommend offering food immediately
before insulin administration to ensure the patient is interested in eating. In addition, for patients receiving Vetsulin,
the first peak of activity provides an excellent buffer against postprandial hyperglycemia.