By Dr. Alison Book, DACVIM Oncology

This is a great question that is commonly asked by our clients. The answer isn’t as easy as a simple “yes” or “no.” Simply put, blood tests are a piece of the puzzle, but in most cases, they don’t tell the whole story.

For many types of cancer in dogs and cats, it is common for routine blood tests such as the complete blood count and chemistry panel to be completely normal. However, there are instances when blood tests can help us diagnose cancer and also help us provide you with the most information about your dog’s or cat’s condition.
When we run blood tests on your pet, here are the common things we’re looking for or trying to rule out:

Cancers that come from blood cells (termed hematopoietic tumors): These can be diagnosed from a blood test in cases when cancerous cells are circulating in the bloodstream. We may see an increased cell count or abnormal looking blood cells.

Cancers that are growing in the bone marrow: When cancer is growing in the bone marrow, it is harder for the bone marrow to do its job- which is to make new blood cells. As a result, we may see decreases in one or more cell lines that are produced here (platelets, white or red blood cells). If blood cells aren’t produced in adequate quantities, it can result in serious problems such as decreased energy, less oxygen being carried in the blood, and increased susceptibility to bleeding or infection.

Syndromes that are secondary to cancer (termed paraneoplastic syndromes): Some cancers can cause secondary changes in the blood stream that will give us a clue that a dog or cat may have a certain type of cancer. Once we know what type of cancer your pet has, we can begin to figure out how to treat it. These changes can be due to substances that are produced by the tumor or because the immune system is abnormally stimulated by the cancer.

Tumors that cause changes in kidney or liver function: When tumors are growing in major organs, we may see changes in enzyme values that would indicate this.

Factors that influence prognosis: Once a cancer has been diagnosed, blood tests may give us information about differences in expected outcomes.

Other concurrent diseases: It is also important to know if your pet has other conditions unrelated to cancer such as kidney or heart disease as these may influence the type of treatments that are recommended for your dog or cat.

At this point, there is no commercially available test that can be performed on the blood that reliably detects all types of cancer. For early detection, routine veterinary visits are still your best bet!