ASK THE VET

Blood tests are a part of cancer diagnosis in pets

4/22/2018

A difficult question that people will pose is whether a blood test can help detect cancer in their pets. Unfortunately, this relatively straightforward question has a complicated answer depending on the type of cancer, but for many types there is no single test that will render a diagnosis.

The most common form of cancer that is usually detected via a blood test is leukemia, which is a cancerous proliferation of white bloods cells in the bloodstream.

Symptoms of leukemia are vague, and typically screening lab work will be sent out with surprising results.

There are different classifications of leukemia that reflect whether it is acute or chronic and the cell line from which they differentiate.

Often these cancers will lead to circulating numbers of white blood cells that are significantly elevated, and a bone marrow biopsy is usually the next step to confirm the diagnosis. The type of leukemia will correlate to how successful treatment might be, and some can have excellent outcomes if caught early.

Some types of cancers in dogs will elevate the levels of calcium in the bloodstream. Lymphoma and some cancers of glandular tissue may lead to higher than normal blood calcium through secretion of a protein that mimics the hormone produced by the parathyroid gland in the neck.

Parathyroid hormone normally maintains the body’s normal level of calcium, and tissues can’t tell the difference between the normal hormone and the similar protein produced by the cancerous cells.

Once an elevated blood calcium is found, a series of test is often needed to find the cancer, which sometimes can be difficult to detect in its early stages. Benign tumors of the parathyroid gland will also produce excess amounts of this hormone, but fortunately some labs now can differentiate between the real hormone and the analogue secreted by cancer cells.

Where the question becomes more complicated is when a tumor has been diagnosed and it becomes important to see if the cancer has spread to other parts of the body. Rarely there may be evidence of major organ involvement, but the majority of cases have normal blood tests.

Chest x-rays, ultrasound, and CT scans are all better methods to attempt and see if cancer has spread or metastasized, which helps determine the success of future treatments.

Generally, blood tests will be part of the data your veterinarian will want to collect if cancer is suspected, but rarely is it a silver bullet that establishes a diagnosis.

Questions for Dr. Gary Thompson can be emailed to askthevet@theblade.com or mailed to The Blade, Attn. Ask the Vet, 541 N. Superior St. Toledo, OH, 43660. Dr. Thompson regrets that he cannot answer individual letters.