Most of the time, you don’t see a copy of your animal’s lab results. When you do, you probably find all those numbers and notations more than a little confusing. The following will help you interpret the results of some of the most commonly performed blood tests.
Defining “Normal”
First, it’s imperative you understand what “normal” means. Every lab develops its own set of normal values based on its patient population. Additionally, patients can have what appears to be an abnormal lab result, yet be totally healthy.
Why? Because normal values are determined using a bell-shaped curve. Approximately 90% of “normal” patients will fall under the bell of the curve. This means 5% of normal patients will fall outside the low end of the normal range and 5% will fall outside the high end.
As an example, let’s look at the BUN test (blood urea nitrogen), commonly used to determine kidney disease. Normal values for most labs are 10 to 30. This means 90% of normal dogs will have a BUN value anywhere from 10 to 30. However, 5% of normal dogs will have a lab value of less than 10 and 5% a value greater than 30. Let’s suppose your dog has a BUN value of 40, which is outside the normal range on the high end. How do you determine if this is normal, or a sign of potentially serious kidney disease? This is where the vet’s medical training and experience come in to determine if it was normal for your dog (in which case it’s nothing to worry about) or abnormal.
First, look at BUN values from prior tests, if available. If your dog has always had BUN values close to 40, it’s probably safe to say this is another normal test. If he has never had this test done before, repeat it in one to two weeks, and compare the value to the current one. Look at other tests of kidney function (creatinine, phosphorus, complete urinalysis, etc.) and see if those were abnormal. If they weren’t, it’s likely your dog’s BUN value of 40 is nothing to worry about. However, re-do the test every few months, especially if you have an older dog since kidney disease is more common in senior animals.
Let’s take a look at some commonly performed tests and what they mean.
Kidney function
BUN
BUN is a common test of kidney function. Unfortunately, it’s also affected by other factors such as intestinal bleeding and dietary protein levels. With kidney disease, the BUN begins to slowly elevate. As mentioned above, mild elevations on a scale of 10 to 20 units can be normal for your dog if other testing of kidney function is also normal. Therefore, an elevated BUN by itself may not be clinically meaningful. However, when combined with other tests of kidney function, an elevated BUN can alert the doctor to a potential problem with the kidneys.
Creatinine
Creatinine is a much more sensitive test of kidney dysfunction. Even small elevations of this enzyme can indicate significant kidney problems. Because it is not affected by dietary protein, any elevation in creatinine levels should alert you to the strong possibility of
underlying kidney disease.
Urinalysis
Many different pieces of information can be derived from a urinalysis. One of the most important deals with kidney function – it’s called the urine specific gravity. If the kidneys are functioning properly, they either dilute or concentrate water presented to them by the bloodstream in the production of urine. If kidney function deteriorates, they are less able to produce dilute or concentrated urine, resulting in an abnormal specific gravity. As is true with blood testing, one abnormal specific gravity may be meaningless. Repeated abnormal values, combined with abnormal blood kidney testing, potentially signals a problem with the kidneys.
Diabetes
While much rarer in dogs than in people, diabetes can still be a serious disease. Fortunately, it is usually easy to diagnose based on laboratory testing and clinical signs. Two tests are commonly used to diagnose diabetes in dogs. The first is the blood glucose test. While levels of blood glucose can become elevated due to other conditions such as stress, they usually indicate a strong possibility of diabetes. A urinalysis can also be used to diagnose diabetes. Normally, glucose does not appear in a dog’s urine. However, as the blood glucose level elevates, some of it spills into the urine. In serious diabetic conditions (called ketoacidosis), glucose levels are very high. So are the levels of a fatty acid called ketones. Combining the results from a blood profile and urinalysis can help the doctor diagnose diabetes.
In rare cases where the results are in a gray area, another blood test measuring fructosamine can be performed. Elevated fructosamine levels may indicate that elevated blood glucose levels are really due to diabetes, and not to any stress experienced by the dog during the office visit.
Liver Function
Even though many doctors incorrectly misdiagnose adrenal disease as liver disease (see next section), true liver disease is thankfully rare in most dogs. The best test for diagnosing liver disease is the ALT (alanine transaminase) test (formerly called SGPT).
Patients can have what appears to be an abnormal lab result, yet be totally healthy. When there’s any sort of trauma/infection/inflammation/cancer in the liver, cell damage occurs and ALT leaks from the cells, causing elevated ALT levels in the blood. Small degrees of elevation can be normal, especially in older dogs (and those taking medications such as corticosteroids or phenobarbital). As is often the case with most blood tests, elevated levels do not tell us the cause of the disease, only that something is traumatizing the liver (infection, inflammation, benign or cancerous lesions, medications, etc.)
Adrenal Function
Overproduction of adrenal gland hormones (particularly cortisol) is one of the most common problems in older dogs. An elevated ALP (alkaline phosphatase) value commonly indicates excess cortisol in the dog’s body, either from overactive adrenal glands or from prescription steroid medications. While ALP values can also be elevated in dogs with liver disease, it is most commonly elevated in those with adrenal disease, especially if other liver tests are normal. Unfortunately, many doctors misdiagnose dogs as having liver disease based on an elevated ALP level, when in fact they actually have adrenal disease.
This is one of the most common diagnostic mistakes I see in clinical practice, and it often results in dogs receiving unnecessary liver biopsies. There are no conventional medications to help dogs with elevated ALP values, but many herbs and homeopathics can be used to try and slow down the development of Cushing’s disease, a condition that occurs if the adrenal glands continue to produce too much cortisol.
Regular laboratory testing is important for your dog, both to determine his normal values as well as allow early diagnosis and treatment of potentially life-threatening diseases. Keep in mind that even “abnormal” blood and urine tests can be totally “normal” for your dog. If there’s any doubt, simply repeating the test in a week or two, or getting a second opinion, can allay any concerns.