Generally, the following screening tests are recommended when diabetes mellitus is suspected: a complete blood count (CBC), a serum biochemistry profile, and a urinalysis.
Why so many tests, can’t diabetes be diagnosed by an elevated blood sugar value alone?
While confirmation of elevated fasting blood and urine glucose (sugar) values is absolutely essential for the diagnosis of diabetes mellitus, these screening tests may give us additional information regarding the severity of the diabetes, about any conditions that may be contributing to the diabetes, as well as detecting complications related to the diabetic state.
Because diabetes is usually diagnosed in middle aged to older dogs, your pet may have other unrelated conditions that need to be managed along with the diabetic condition. These screening tests will hopefully alert us to any such conditions.
So what might these screening tests indicate if my dog has diabetes mellitus?
The complete blood count (CBC) involves evaluation of the red blood cell, the white blood cell, and the platelet components of a blood sample.
Often with uncomplicated diabetes mellitus, these components are within the normal range. However, changes may occasionally be seen in the red or white cell values.
Although most diabetic animals drink large quantities of water, they are losing a lot of body water because they produce such dilute urine. Therefore your pet may actually be dehydrated. Dehydration can be indicated on the CBC by increases in the packed cell volume (PCV – the proportion of the blood volume that is actually occupied by red blood cells) as well as increases in the total red blood cell count.
In some severe diabetic states, lysis (rupture) of red blood cells within the blood stream may occur because of the loss of electrolytes. A reduction in the PCV and red blood cell count will be seen on the CBC if this is occurring.
Infections, particularly urinary tract infections, are common in diabetic patients. The presence of an infection may be indicated on the CBC by an increased number of white blood cells.
The serum biochemistry profile requires a separate blood sample from which the serum (the liquid portion of blood) is separated from the cellular portion. Serum contains many substances including glucose, enzymes, lipids (fats), proteins, and metabolic waste products.
Determination of the serum glucose concentration is vital to the diagnosis of diabetes mellitus. A fasting sample is best because even in healthy dogs, the serum glucose may be mildly increased for up to four hours following a meal. Most diabetic dogs will have moderate to marked increases in fasting serum glucose concentrations. These increases are usually far greater than those mild, transient increases noted after eating.
Occasionally we may see changes in serum electrolytes. Electrolytes are the salt and metallic components of serum. They are involved in many of the body’s daily functions, for example nerve conduction and maintenance of proper hydration.
Because of the large volume of dilute urine that diabetic dogs produce, excessive amounts electrolytes may be lost in the urine. Such losses may result in rare but serious complications. For example, severe deficits in the electrolyte phosphorus may result in the rupture of red blood cells within the blood stream.
The liver related enzymes ALT (alanine aminotransferase) and AST (aspartate transaminase) may be increased mildly in diabetic dogs. These increases may reflect mild liver cell damage that is related to decreased blood flow as a consequence of dehydration. Alterations in lipid (fat) metabolism as a consequence of diabetes may also contribute to increases in these liver enzymes. This altered fat metabolism may be noted by increases in serum cholesterol concentrations.
A urinalysis is necessary for the diagnosis of diabetes mellitus. Urine from healthy dogs does not contain any glucose (sugar) even shortly after eating. Generally, the finding of glucose in the urine (called glucosuria) as well as increased blood glucose levels (called hyperglycemia) in a dog with appropriate clinical signs is confirmatory for diabetes mellitus.
Other important features of the urinalysis that need to be evaluated in diabetic animals include evidence of urinary tract infection. The presence of glucose in the urine makes conditions ideal for bacterial growth; therefore urinary tract infections are common. The urine is evaluated for the presence of red blood cells, white blood cells and bacteria. A culture of the urine may be indicated to determine what types of bacteria are present and the most appropriate antibiotics that can be used to treat the infection.
The presence or absence of ketones in the urine should be evaluated in diabetic animals. Ketones are by-products of fat metabolism. Increased utilization of fat occurs in diabetic animals because their insulin deficiency results in poor utilization of carbohydrates as an energy source. Depending upon your dog’s clinical signs, the presence of ketones in the urine may indicate a more severe or long-standing case of diabetes.
Now that my dog has been started on insulin therapy what monitoring tests can we use?
When insulin therapy is first started, we will need to monitor your dog’s blood glucose values frequently. Typically this involves serial blood or serum glucose determinations, often in the form of a glucose curve.To obtain a glucose curve your dog will need to be hospitalized for the day. He will be fed his usual amount of food and given his usual insulin dosage. Blood samples will then be taken every 2 hours throughout the day, and the results will be plotted on a graph. This will show how well the insulin is controlling his blood glucose, the time of peak effect of the insulin, and the duration of action of the insulin.
While further adjustments in your dog’s insulin dosage will undoubtedly need to be made, the blood glucose curve is valuable in letting us know the approximate type of response your dog has to the insulin product that he has been started on.
One of the most important things you can do for your dog is to simply monitor his appetite, water consumption, energy level, and urine output.
Any changes may signify the need for additional testing and/or adjustments in the insulin dosage (it is very important that you do not make adjustments in dosage without first consulting your veterinarian).
Additional home monitoring can involve the evaluation of urine for the presence of glucose. This involves ‘catching’ a urine sample in a clean container and simply dipping a urine test strip that has an indicator pad for glucose. After a specified time interval, the glucose level can be read.
At the beginning of insulin therapy, more frequent (daily) monitoring is indicated. The presence of large amounts of glucose for two or three days in a row, or the complete absence of glucose may indicate the need for adjustments in insulin dosage.
Once your dog’s optimal insulin dosage has been determined and his diabetes is well regulated, monitoring may involve weekly ‘spot checks’ of urine for the presence of glucose.
Serum fructosamine concentrations are another way of evaluating your dog’s response to insulin therapy. Fructosamine forms through the irreversible binding of glucose to proteins in your dog’s blood stream. The higher the blood glucose, the greater the amount of fructosamine formed. Similarly, the lower the blood glucose, the smaller the amount of fructosamine formed.
Fructosamine is measured from a single blood sample. No special preparation such as fasting, and no timing of blood samples is required. Serum fructosamine provides us with a retrospective view of the average blood glucose concentration that your dog has achieved over the past 2 to 3 weeks. Therefore it is extremely helpful in the long-term monitoring of diabetic patients.
However, recent changes in blood glucose concentrations will not be detected with the serum fructosamine test. Therefore if your dog is showing any behavioral changes that might signal changes in his insulin requirements, then a direct blood glucose test will be more appropriate.