Preparing your pet for laboratory testing varies according to the type of test being performed.
The two most-commonly performed tests, fecal flotation and heartworm test require no preparation at all. However, to save your pet from the discomfort of staff having to obtain a stool specimen with a rectal probe, bring in about a tablespoon of feces not more than 24 hours old.
For purposes of this article we will define the term “fasting” as no food and no water for 12 hours.
Patients having a CBC or Complete Blood Count are usually not fasted. As the CBC is mainly concerned with the cells in the bloodstream, it is minimally affected by food and water intake.
The Chemistry Profile, on the other hand, is greatly affected by both food and water consumption and the best results are obtained when the patient is fasting. An exception includes pets known to have reduced kidney filtration, who should never have water restricted.
Complete urinalysis should also be performed fasted. Partial U/A, in which a single parameter is being tested and it is not affected by eating and drinking would be an exception, as would above-described kidney failure patients.
Preparation for urinalysis can vary by both doctor and patient, so be sure to ask for your pet’s doctor’s guidance. The usual approach is to not allow the pet to urinate for about 6 hours. For an early-morning appointment, that can mean empty the bladder the last thing before bedtime, then don’t allow the pet to urinate until the doctor obtains the urine. Some pets may need to be confined to a small area, such as a bathroom or pet carrier. Carriers work well for keeping cats from their litterboxes, too. Restricting a pet’s available space invokes the natural tendency to avoid soiling a close-by area.
Lipemia, or excessive fat in the bloodstream, is a more common problem in dogs than cats. Certain individuals and certain breeds are more likely to exhibit this trait. The miniature schnauzer is the poster child for lipemia. When lipemia is present certain results may give false returns. Multiple parameters in the chemistry profile are affected, as well as certain individual tests. Patients exhibiting lipemia may require longer periods without food prior to testing.
The Thyroid Test is not affected by fasting, but is altered by timing. Best results occur 4-6 hours after giving the pill.
Some medication monitoring is unaffected by timing. Phenobarbital and Potassium Bromide are used separately or together for seizure control. After approximately two months of regularly-scheduled administration both reach a steady state in which blood levels vary little during a 24-hour period.
Interestingly, while blood sugar levels vary from moment to moment, a test called fructosamine is available which gives us a reading that represents average blood glucose over an approximate 14-day time period. This test is valuable for determining control of a diabetic’s insulin regulation as well as to separate excitement-induced hyperglycemia from elevated blood glucose associated with diabetes.
Regardless of the laboratory test being performed, ensure that you contact your pet’s doctor to be 100% clear on what your pet’s preparation instructions should be.
See you tomorrow, Dr. Randolph.