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Why Your Pet Needs an Annual Blood Test

blood testing from vet in lakeland fl

“Do you really need to do bloodwork on him/her?”

I hear this question a lot.

We may recommend bloodwork for your pets for a wide variety of reasons. Your pet’s blood can tell us a lot about what’s going on with their health. Sure, we have digital x-ray and ultrasound, and they can help, too- but the blood holds a treasure trove of information. Often, it is the best diagnostic tool we have at our disposal. We know some tests can be expensive, but please know that these tests are needed so we can make an accurate diagnosis and treat your pet’s ailment with the proper treatment the first time- whether it be short or long-term. We never will suggest bloodwork just to inflate a bill. It will never happen. Promise.

In this blog, I want to focus on senior pets- for most breeds of dogs and cats- we’re talking about pets over the age of seven. I’ll cover younger pets in an upcoming article.

Why is it important for my senior pet to get bloodwork?

As I mentioned earlier, your pet’s blood is like gold. It holds valuable information which can tell us how your pet’s organs are working. Below are just some of the things we’re concerned about as your pet ages- and doing bloodwork will be able to tell us how they’re doing.

  • Kidney disease
  • Decreased kidney function
  • Liver Disease
  • Pancreatic Inflammation
  • Thyroid Disorders
  • Adrenal Disease
  • Diabetes
  • Infection
  • Anemia

Early Detection is Critical

We suggest doing bloodwork every year for senior pets. When we run tests on your healthy pet’s blood the first time- it gives us a starting point to refer back to. This allows us to prescribe, modify or alter medications, special diets or recommend lifestyle adjustments to keep them healthy over the long term.

Organ function may begin to decline at any time in your pet’s life, but it is most likely to happen as they reach their senior years. Early detection is critical, since most of the conditions mentioned above are not visible until it is too late. For instance, Kidney disease does not begin showing symptoms until close to 2/3 of the kidney function is lost. If caught early, kidney disease can be kept in check with medication and with some simple modifications to diet and lifestyle.

What is a Senior Profile?

 As your pet reaches their ‘golden years’, we will begin talking about wanting to do a blood test called a Senior Profile– also called a senior wellness profile. A senior profile is actually a batch of tests which will help us identify potential problems commonly found within senior pets. The tests included in a Senior Profile:

  • CBC (Complete Blood Count)
  • Urinalysis
  • Total T4
  • Superchem
  • Heartworm Antigen

Let’s break down these tests- what they are and what they are telling us! We’re going to be a little scientific here, sorry. I don’t want to bore you with a bunch of science, but all of these things are really, really important.

(This information is also available on our website under medical conditions. Content courtesy of Lifelearn)

What is a Complete Blood Count?

The Complete Blood Count, commonly called a “CBC” is a routine blood test that is used in all stages of health and illness. It is a simple test that gives information about the different cell types in the blood and can indicate the presence of many forms of disease. Most of the blood cells come from bone marrow, so the CBC can also be used indirectly to assess the health of the bone marrow.

How is a CBC performed?

A small sample of blood is collected from the pet and placed in a special tube that prevents the blood from clotting. The sample is then put in a machine called an automated blood analyzer, which counts the different cell types and describes various characteristics of the cells. In addition, a drop of blood is spread thinly on a glass slide creating a blood smear. This is stained with special dyes, and examined under the microscope to look at the appearance of individual cells.

What does a CBC measure?

The CBC provides information about the three types of cells found in blood. They are red blood cells (also called erythrocytes or red cells), white blood cells (also called leukocytes or white cells), and platelets (sometimes called thrombocytes). Details are reported on the number, size, and shape of each cell type, as well as any variation in appearance.

What are red blood cells and why are they important?

Red blood cells are the most numerous cells in blood by far, and give blood its red color. They are responsible for carrying oxygen from the lungs to the tissues of the body. They can do this because of a special protein called hemoglobin that is found in each red blood cell. As blood is pumped through the lung, oxygen moves into the red cells and binds tightly to hemoglobin. When the blood is pumped out through the body and into the tissues, oxygen is released from hemoglobin and allowed to leave the red cells to enter the cells of the tissues.

What does the CBC tell us about red blood cells?

a) Numbers:

The CBC reports three different red cell measurements: Red Blood Cell count (RBC), hematocrit (HCT) and hemoglobin (HGB). These measurements provide information about how many red cells are present and how much hemoglobin is available. A decrease in either the red cell count or the amount of hemoglobin is called “anemia.” There are many causes for anemia, and although the CBC may provide clues, further investigation is almost always required to reach a diagnosis. By comparison, a mild increase in the number of red cells is relatively common and usually indicates that the pet is dehydrated or excited. This change is usually temporary and is not worrisome. In very rare cases a persistently high red blood cell count can signal a bone marrow disorder.

b) Size:

The size of the red blood cells sometimes provides clues about a disease. For example, larger red cells can be seen with vitamin deficiency and bone marrow disease etc. Smaller red blood cells can be found with iron deficiency and immune system problems. Sometimes the red cells are normal size, but there just aren’t enough of them. This suggests longstanding illness such as ongoing kidney disease, persistent inflammation, or cancer.

c) Color and shape:

The color and shape of the erythrocytes are additional details that help in the diagnosis of disease. For example, an erythrocyte with a bluish tinge is called a polychromatophilic erythrocyte (often shortened to polychrome); it is a young red cell newly released from the bone marrow and it is slightly larger and bluer than older red cells. In an anemic animal, finding polychromes in the blood is a good sign because it signals that the bone marrow is responding to the anemia by working hard to produce new red blood cells. Sometimes a special dye is used to count polychromes, and the number is reported as a reticulocyte count. This provides the same information as counting polychromes, but it is more accurate.

There are many red cell shape changes that have been associated with various diseases. The changes are rarely diagnostic by themselves but they can provide clues to the nature of the underlying disease.

What are white blood cells and why are they important?

White blood cells or leukocytes (“leuko” means ‘white’) are essential to help protect the body against infectious organisms such as bacteria and viruses, and also against foreign material that may enter the body.

“Think of white blood cells like the “armed forces” of the body…”

It may help to think of white blood cells as the “armed forces” of the body. Instead of the army, navy, and air force, the body’s armed forces have five branches represented by different types of white blood cells called neutrophils, lymphocytes, monocytes, eosinophils, and basophils. The different groups of leukocytes work independently and in combination, depending on the problem that is present.

What does the CBC tell us about white blood cells?

a) Numbers:

The automated analyzer counts the total number of white blood cells and reports a White Blood Cell count (WBC). This gives an indication of the pet’s overall level of protection against infection. The analyzer then subdivides the WBC and counts the number of leukocytes in each of the five divisions. The resulting five numbers together are called the “differential.”Changes in the distribution of leukocytes across the differential can provide information about the type and severity of inflammation, possible causes of the inflammation, and whether the bone marrow is able produce enough white blood cells. Sometimes the white blood cell count is extremely high or extremely low; either of these changes may signal severe infection or indicate serious bone marrow disease, including cancer.

b) Appearance:

The appearance of leukocytes can indicate whether the body is overwhelmed by infection or is handling a crisis properly. Leukocyte appearance can indicate the presence of toxins or signal that the immune system has been activated. The presence of bizarre-looking or abnormal cells is often a sign of serious bone marrow disease including cancer.

What are platelets and why are they important?

Platelets are tiny cell-like structures that are present in large numbers blood and serve as the first line of defense against bleeding. They are continually on guard to seal microscopic injuries on the inside of blood vessels, and they are the first to respond to minor wounds. For example, when you get a skin scratch or paper cut, or prick your finger with a pin, it is the job of the platelets to stop the bleeding. It is critical to maintain adequate numbers of platelets in the blood.

What does the CBC tell us about platelets?

a) Numbers:

The automated analyzer reports the number of platelets in the blood, which gives an indication of the body’s ability to stop minor bleeding. If the platelet count falls below a certain critical level, then widespread spontaneous bleeding may occur. A low platelet count may be caused by a variety of diseases such as recent infection, serious systemic illness, immune disorders, or bone marrow disease. An increased platelet count is commonly associated with simple excitement or exertion, although a high platelet count may be seen when the marrow is working hard to repair a shortage of platelets. In very rare cases, extremely high platelet counts may indicate underlying bone marrow cancer.

b) Size:

A platelet’s size is generally related to its age; young platelets are large and plump while older platelets are generally smaller. The presence of large, plump, young platelets indicates that the bone marrow is actively producing new platelets. This is an important finding and in a pet with a low platelet count, it is a clue about the underlying disease.


Very rarely, bizarre-looking abnormal platelets may be found; these are often a sign of serious bone marrow disease including cancer.


What is a urinalysis?

Urinalysis is a routine test that reports the physical and chemical properties of urine. It is used mainly to assess the health of the kidneys and urinary system, but it can also reveal problems in other organ systems, and is important for diagnosing metabolic disease such as diabetes mellitus. It is a valuable test in both healthy and sick animals and should be included in any comprehensive evaluation of a pet’s health.

On a related subject, check out my blog on why your pet’s poop is so important in another blog called “The Scoop on Your Pet’s Poop”.

The T4 test-

No, Arnold Schwarzenegger isn’t making a 4th Terminator movie… We’re checking out your pet’s thyroid- specifically if they may be hyper or hypo thyroid.

The thyroid gland produces both thyroxine (T4) and triiodothyronine (T3) hormones. Thyroxine (T4) is the primary hormone produced by the thyroid gland in response to stimulation by the pituitary gland. Although it is also produced by the thyroid gland, T3 is primarily made in the tissues by the breakdown of the T4 hormone. Therefore, evaluation of T3 levels is not commonly useful in the diagnosis of hypothyroidism.

“A ‘feedback system’ exists between the thyroid gland and the pituitary gland.”

A ‘feedback system’ exists between the thyroid gland and the pituitary gland. When T4 concentrations in the blood are low, the pituitary sends a signal to the thyroid gland using thyrotropin, also known asthyroid stimulating hormone (TSH), prompting the thyroid gland to produce more T4. When T4 levels in the circulation are adequate, the pituitary decreases its production of TSH, thereby reducing the production of T4.

“If the total T4 concentration is well within the normal range, then your dog is not hypothyroid.”

Total T4 (Thyroxine): T4 circulates in the blood in two forms; one form of the hormone is bound,or attached to proteins in the blood, while the other form circulates freely within the blood stream.Total T4 measures both forms of the hormone in a blood sample. If the total T4 concentration is well within the normal range, then your dog is not hypothyroid. If the total T4 concentration is at the low end or below the normal range, and your dog has supportive clinical signs, then hypothyroidism is likely. Unfortunately, there are conditions other than hypothyroidism that may cause the total T4 value to be reduced. These conditions include the presence of another illness or the administration of some drugs, such as anti-inflammatory medications. Your veterinarian may be able to measure total T4 levels in the veterinary office.

Free T4 (free thyroxine): This test measures the amount of the free thyroxine hormone in a blood sample. Free T4 is less affected by the presence of other illnesses or drug therapies. If the free T4 is within the normal range, then your dog does not have hypothyroidism. If the free T4 is below normal range, and your dog has supportive clinical signs, then hypothyroidism is likely.

The disadvantage of this test is that the free T4 assay requires the use of a special technique that is only available at a referral laboratory, is more costly and takes longer to get a result. Therefore, it is more common to evaluate a blood sample for the total T4 level. If the results of the total T4 are ambiguous, then a free T4 test can be done.

“TSH … needs to be interpreted along with a simultaneously measured total T4 or free T4 result.”

Endogenous TSH (thyrotropin):TSH is produced by the pituitary gland. In hypothyroid dogs, the concentration of TSH may be increased as the pituitary tries to stimulate the thyroid gland to increase hormone production. TSH can be measured in a blood sample but the result needs to be interpreted along with a simultaneously measured total T4 or free T4 result. Measurement of TSH requires sending the blood sample to a referral laboratory.

“A normal TSH, free T4, and total T4 effectively rules out the possibility of hypothyroidism.”

A normal TSH, free T4, and total T4 effectively rules out the possibility of hypothyroidism.
Although there are other tests available for the assessment of thyroid function, the above tests are the most commonly used for the diagnosis of hypothyroidism and yield the most diagnostic information.

Are there other uses for the measurement of total T4?

In addition to being used for the diagnosis of hypothyroidism, total T4 can be used to monitor therapeutic levels of thyroid hormone supplementation if your dog requires thyroid hormone replacement therapy.

Additionally, in the very rare cases of suspected thyroid gland cancer, total T4 can be monitored to determine whether the cancerous tissue is producing excessive amounts of thyroid hormone.

Superchem- what is it, and what do you learn from it?

While a CBC (complete blood count) tells us about the cells contained in the blood, the Superchem tells us about the chemicals and enzymes within the blood. The results can give us important information about the general health of the kidneys, liver and pancreas. It will also tell us about blood sugar levels (critical for diabetes detection) and electrolytes like potassium, calcium and sodium.

Heartworm Antigen

south tampa dog getting a blood testJust because your pet is getting older doesn’t mean they are no longer at risk of Heartworm disease. Even if your pet is on Heartworm Prevention, we always want to ensure that your pet is Heartworm-free.

Please keep in mind that these tests are not just for senior pets. All of these tests described here are included in a Senior Profile- as they include everything we want to check within your senior pet (well, usually everything). We will often run some of these tests individually for younger pets, such as the CBC for general illness- or the T4 if we suspect a thyroid issue. We literally have dozens and dozens of tests we can run- which ones we choose are based on your pet’s presenting symptoms.

If you have any questions about bloodwork, we’d enjoy discussing them with you during your next visit with your pets!