Veterinary Clinical Sciences, Louisiana State University, Baton Rouge, LA, USA
Monitoring and Insulin Dosage Adjustment
Increases in the insulin dose should be based on the presence of clinical signs (polyuria and polydipsia, changes in body weight) combined with proof of hyperglycemia and/or unacceptable glycemic control (continuous glucose monitoring, blood glucose [BG] curves, glycated proteins [fructosamine, HbA1c]). Prior to recommending an insulin dosage increase, one should consider the severity of clinical signs, degree of hyperglycemia, size of the animal (typically increase by 1 unit/dose in cats/small dogs and 2–3 units/dose in larger dogs), and the current insulin dose (consider causes of insulin resistance or need to change formulations when dose is >1.5–2 U/kg). In order to avoid overdosing and hypoglycemia, it is recommended to wait at least 7–10 days following an increase in the insulin dose before considering another dosage increase.
Urine Glucose Quantification
Semi-quantitative urine glucose measurement is a crude assessment of glycemic control that confirms hyperglycemia in excess of the renal threshold (180–220 mg/dL in the dog and 200–280 mg/dL in the cat). The detection of glucosuria is of limited utility in dogs because given the current approach to managing canine diabetes, even well-regulated dogs would be expected to exceed the renal threshold for glucose at some point during the day. In most cases, it is possible to obtain similar clinical information by questioning the owner about observed polyuria and polydipsia. If urine glucose is used for monitoring in dogs, the author recommends only using it to assess for over supplementation/persistent hypoglycemia (i.e., recommend decreasing the insulin dose after documenting the absence of glucosuria) and not as a guide for increasing the insulin dose. Urine glucose measurement is no longer recommended as the only assessment of glycemic control in dogs and better monitoring techniques are available.
Urine glucose quantification can be used to assess glycemic control in cats because it is possible to safely maintain their blood glucose below the renal threshold (∼250 mg/dL) for most/all of the day with long-acting insulin formulations.
As a result, the presence of glucosuria suggests inadequate glycemic control and the need for more insulin. Urine glucose monitoring cannot be used to detect/confirm persistent hypoglycemia in cats that are in a diabetic remission (non-insulin dependent state) receiving insulin so blood or interstitial glucose monitoring must be used to confirm remission.
Blood Glucose Curves
Despite substantial day-to-day variability in BG curve results, a complete 12-hour BG curve can provide useful information when evaluating a poorly regulated diabetic, especially if continuous glucose monitoring is not an option. Blood glucose data collected in the home environment is likely more representative of the actual glycemic control than monitoring in the clinic or hospital. This is especially true in cats because of stress hyperglycemia. The author does not recommend in clinic/hospital monitoring for cats even if it appears they are tolerant/”not stressed.” It is recommended that BG curve data from multiple days during a 2–3 week period be evaluated prior to recommending significant changes such as a change in the insulin formulation. This will allow the clinician to evaluate trends rather than a single BG curve which may not be an accurate representation of the glycemic control. Routine blood glucose monitoring also plays an important role in detecting subclinical hypoglycemia, the occurrence of diabetic remission, and/or the return to an insulin-dependent state in cats.
Home Blood Glucose Curve Protocol
- Use a hand-held glucometer that has been validated for use in dogs and cats
- Blood glucose before food and insulin administration
- Feed and administer insulin
- Blood glucose 1 hour after food and insulin, then every 2 hours (every 4 hours in cats receiving long-acting preparations) until the next dose of insulin
Continuous Glucose Monitoring
The FreeStyle Libre continuous glucose monitoring system provides a readily available, cost-effective way to continuously assess glycemic control over a 14-day period. The system measures the interstitial glucose, stores up to 8 hours of data, and does not require blood sampling for calibration.
Continuous glucose monitoring is the recommended assessment method for any challenging diabetic and has replaced blood glucose curves for monitoring in most diabetics in the author’s practice.
The fructosamine concentration provides an estimate of glycemic control/average blood glucose concentration during the preceding 1–3 weeks. Factors or conditions known to affect the fructosamine concentration include hypoproteinemia, hyperlipidemia, azotemia, and hyperthyroidism. The fructosamine concentration is infrequently measured in our practice and may provide additional information about glycemic control in fractious diabetic cats that will not tolerate home blood glucose curves or continuous glucose monitoring or to establish a diagnosis of diabetes mellitus.
Glycated hemoglobin or HbA1c plays an important role in the detection of pre-diabetes and assessment of longterm glycemic control in people. Although previously studied in dogs and cats, species differences affected the performance of human assays and greatly limited the utility of this monitoring technique. A canine and feline specific HbA1c (A1CARETM, http://baycomdiagnostics.com/) test has been developed and is now commercially available. Glycated hemoglobin provides information about the average blood glucose during the preceding ∼110 days in the dog and ∼70 days in the cat (lifespan of the red blood cell). This test is expected to prove useful in screening and early detection of diabetes/pre-diabetes and will likely provide a better assessment of long-term glycemic control than fructosamine.
References are available upon request.