Staging for Canine and Feline Cancer Patients – The Blood Testing Stage

Now that you’ve read The Importance of Staging for Pets With Cancer, Part 1, it’s time to move on to the next group of diagnostics used when staging cancer patient.

Staging is the process of combining a veterinarian’s physical examination with a variety of diagnostic tests to help determine if the presence of cancer is detectable or not. If the cancer is undetectable, then a pet can still be considered to be in remission. If the cancer is detectable, then the pet is not in remission.

The tests used by the overseeing veterinarian vary depending on the individual nature of the patient’s case and sometimes on the owner’s financial situation or desires to have a pet go through certain diagnostic procedures, or not, but some tests are more common than others.

This article will cover blood testing.

Types of Blood Tests for Cancer Patients

The blood tells us so much about the internal functioning of our pets’ bodies. Yet, blood testing doesn’t reveal a complete picture, which is why evaluating the blood is just one of the many tests we veterinarians often recommend when striving to determine a pet’s state of wellness or illness.

Generally, blood is relatively plentiful and easily accessible through venipuncture, which is the process of drawing a sample from one of the body’s many veins. Smaller dogs and cats commonly present a challenge due to their smaller and more fragile veins and the challenges faced during restraint, making it difficult to attain a sufficient sample. Large dogs are sometimes as much or more of a challenge to restrain than their petite counterparts and they can have veins that are more resistant to attempted puncture by a needle, though they readily give up substantial volumes of blood.

Common tests run on blood include a blood chemistry test and a complete blood count (CBC). There are many more tests that can be done, but for the purposes of this article I want to focus on those that are most commonly used when evaluating cancer patients. I run blood testing on Cardiff every 14-21 days, which is always done the day before he receives intravenous or oral chemotherapy.

What Blood Chemistry Testing Reveals

Blood must be centrifuged (spun down) to separate the serum from the red and white blood cells and platelets in order to perform chemistry testing, which assess values pertaining to the kidneys, liver, gall bladder, intestines, pancreas, blood proteins, glucose, electrolytes, calcium, thyroid glands, and more.

Blood values pertaining to the kidneys, liver, red and white blood cells, and platelets are those that are most-crucial in determining how well a pet is handling chemotherapy treatments and attaining a general sense of whole body health.

Blood urea nitrogen (BUN), creatinine (CREA), phosphorous (PHOS), and symmetric dimethylarginine (SDMA) are all tests that shed light on kidney function. Typically, levels above the high threshold of normal for the above tests cause concern for underperforming kidneys and can necessitate a modification in the treatment protocol. Fortunately, decreases don't generally create cause for concern, but still merit consideration and reevaluation.

Alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gabba glutamyl transferase (GGT) yield crucial information about liver function. An elevated ALP indicates liver inflammation, while ALT, AST, and GGT increases indicate liver cell damage. Decreases in the above values aren’t as concerning as increases but can still indicate the presence of certain liver diseases.

Bilirubin reveals information about the gall bladder, which is a blind sac that sits among the liver lobes and has a bile duct that empties into the intestines. Elevations in bilirubin can occur as a result of gall bladder, liver, intestinal, or other diseases, like hemolysis (red cell damage).

Amylase, lipase: pancreatic lipase can shed light on intestinal and pancreatic function. Increases in amylase and lipase typically indicate intestinal inflammation and are non-specific for pancreatic inflammation. Pancreatic lipase gives more reliable information about the pancreas and can be increased during bouts of pancreatitis (pancreatic inflammation). Decreases in amylase, lipase, and pancreatic lipase are not typically cause for concern.

Total protein (TP) is an important value that takes into consideration all of the blood proteins, including albumin (ALB) and globulin (GLOB). Both elevations and decreases in TP, ALB, and GLOB merit concern. Elevations are commonly seen with infection, inflammation, cancer, and dehydration. Decreases can indicate blood or protein loss through the intestines, kidneys, and elsewhere, lack of absorption of nutrients, or even endocrine (glandular) diseases like hypoadrenocorticism (Addison’s disease).

Blood glucose (GLC) should be kept within a normal range and levels that are high (hyperglycemia) or low (hypoglycemia) are cause for concern. Hyperglycemia can occur at times of stress, injury, or illness. Diabetes mellitus is the primary endocrine disease that causes hyperglycemia. Hypoglycemia may happen when the body’s available sugar-stores in the liver have become depleted or aren’t accessible due to hormonal imbalances (Addison’s disease), blood borne bacterial infections (sepsis), and even certain types of cancers (insulinoma, an insulin secreting cancer).

Electrolytes include Sodium (Na), Potassium (K), and Chloride (Cl), all of which are elements that play crucial roles in maintaining normal cellular function. Both increases and decreases are concerning and can be seen with a variety of ailments related to cancer, glandular diseases (kidney, liver, etc.), or even day-to-day activities (exercise, etc.).

Calcium (Ca) is another element that has a vital role in bodily function for muscular contraction, bone formation, and cellular maintenance. Elevated calcium (hypercalcemia) is a serious concern as it can occur as a result of consuming a diet that is too rich in calcium, overconsumption of calcium supplements, or secondary to kidney failure or certain types of cancers (carcinoma).  

Decreased calcium (hypocalcemia) is also a cause for concern and may happen when insufficient calcium is consumed, when ALB levels are too low, after exposure to certain toxins (ethylene glycol, or antifreeze), or other causes.

The thyroid glands, as a pair, reside in the tissue on the underside of the neck and produce hormones that regulate metabolism and other bodily functions. Under-functioning thyroid (hypothyroidism) is an immune-mediated disease that commonly occurs in adult to senior dogs and causes alterations in multiple blood tests, including T4, Free T4 by ED, and cTSH.

Decreases in T4 can also occur as part of a phenomenon called euthyroid sick syndrome—low levels of thyroid hormone unrelated to hypothyroidism—which can develop when a pet is taking certain medications. The presence of many ailments can cause a decrease in T4, which is why veterinarians should perform multiple blood tests for thyroid function when there is suspicion for hypothyroidism.

Over-functioning thyroid (hyperthyroidism) is a glandular condition where thyroid cells divide at a rapid rate and produce elevated thyroid hormone levels; common in middle-aged to senior cats and in dogs having thyroid cancers (adenocarcinoma).

Complete Blood Count (CBC)

CBC is an interesting test that sheds light on the body’s ability to transport oxygen, the immune system’s status for fighting disease and managing inflammation, and the blood’s ability to clot. A CBC must be performed a short time before chemotherapy is given to ensure the patient doesn’t have key changes that would prevent the veterinarian from administering cancer-fighting drugs. The main components evaluated by a CBC include Red Blood Cells (RBC), White Blood Cells (WBC), and Platelets (PLT).

RBCs are crucial for oxygen delivery via hemoglobin (HGB). RBC elevations (polycythemia) are commonly seen with dehydration. This typically doesn’t merit great concern except for the lack of water to provide sufficient dilution to remove metabolic wastes from the body and to permit the blood to smoothly flow through the arteries and veins to deliver oxygen, nutrients, and other crucial substances to body tissues.

A decreased RBC level (anemia) is greatly concerning and can occur as a result of the presence of cancer or other diseases (kidney failure, etc.), as an undesirable side effect of some forms of chemotherapy, after toxic exposures (binging on onions/garlic, etc.), or other causes.

WBCs are key players in helping the immune system to fight cancer, infections, and to manage inflammation and tissue damage all over the body. There are cancers of the WBCs such as Cardiff’s T-Cell Lymphoma, where WBC DNA has been altered and cells proliferate in a manner that lacks a turn-off switch.

So cancer may actually cause a pet’s WBC count to elevate (lymphocytosis) or decrease (lymphopenia), as can having an infection, inflammation, or a variety of ailments. Additionally, chemotherapy can negatively affect production of WBCs from the bone marrow and can cause a reduced WBC count on a CBC.

PLTs are the cells that form blood clots, so they serve a vital function in ensuring that the blood supply doesn’t seep out of the arteries and veins into the outside world or become sequestered in an abnormal location like the lungs, skin, or other organs.

Decreased PLT counts (thrombocytopenia) can occur as a result of cancer, infections (tick borne diseases), chemotherapy, toxic exposures (Brodifacoum rodenticides), immune mediated diseases (Immune Mediated Thrombocytopenia, or IMTP), or other causes.

Elevated PLT counts (thrombocytosis) may occur due to bleeding from trauma, toxic exposures, or certain endocrine conditions like Hyperadrenocorticism (Cushing’s Disease).

I spend a lot of time assessing my patients’ blood values and am keenly interested in the meanings behind both mild and severe changes seen in blood tests. The images here are of one of Cardiff’s pre-chemotherapy IDEXX blood tests, which shows both normal and abnormal values.

(Click images for larger view)

Some of his abnormal values are just below the threshold of normal and don’t create great concern but are being closely monitored by me and his veterinary oncologist, Dr. Avenelle Turner of the Veterinary Cancer Group (VCG).

Image: Red and White Blood Cells in the Blood Stream / Sebastian Kaulitzki

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Blood work: What it means and why your pet needs it (Part 1: The CBC)