What tests are suggested for the diagnosis of diabetes mellitus?
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, other screening tests may give us additional information regarding the severity of the diabetes, any conditions that may be contributing to the diabetes, and any complications related to the diabetic state.
"Diabetes is usually diagnosed in middle aged to older cats, your pet may have other unrelated conditions..."
Because diabetes is usually diagnosed in middle aged to older cats, your pet may have other unrelated conditions that need to be managed along with the diabetic condition. These screening tests will usually alert us to any such conditions.
What might a CBC indicate if my cat has diabetes mellitus?
The complete blood count (CBC) evaluates the red blood cells, the white blood cells, and the platelet components of a blood sample.
With uncomplicated diabetes mellitus, these components are often 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 still lose 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 numbers 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.
What might a serum biochemistry profile indicate if my cat has diabetes mellitus?
The serum biochemistry profile is performed on a separate blood sample from which the serum (the liquid portion of blood) has been separated from the cellular portion. Serum contains many substances including glucose, enzymes, lipids (fats) proteins and metabolic waste products.
"Cats present us with a unique challenge because their glucose concentrations can become markedly increased simply due to stress."
Determination of an elevated serum glucose concentration is vital to the diagnosis of diabetes mellitus. However, cats present us with a unique challenge because their glucose concentrations can become markedly increased simply due to stress. The stress of a veterinary office visit or the mild restraint associated with obtaining a blood sample may significantly increase your cat's serum glucose value. Blood glucose will also be mildly elevated for several hours following a meal. Therefore, confirmation of diabetes may require more than one blood sample collected over a period of several days.
Alternatively, diabetes may be diagnosed by an elevated serum fructosamine test. This test is described below.
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 cats produce, excessive amounts of 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 cats. These increases may reflect mild liver cell damage that is related to decreased blood flow due to dehydration.