What Do All Those Laboratory Tests Tell Me About My Cat's Health?

Published Aug. 19, 2013

During the course of a routine veterinary examination, your veterinarian will conduct a thorough physical examination, checking your cat from nose to tail. However, your veterinarian will also likely recommend performing routine blood and urine testing for your cat as well. What can these blood and urine tests show that a physical examination might not? Let’s talk about some of the specific blood tests and why they are important. (We’ll talk about the urine tests in an upcoming post.)

A basic blood screen will likely consist of a complete blood count (CBC) and a blood chemistry profile. In addition, your veterinarian may recommend testing for thyroid hormone levels. Feline leukemia and/or feline AIDS testing may also be recommended, particularly if your cat’s leukemia and AIDS status is unknown. But exactly what are these tests and what do they look for?

A complete blood count examines your cat’s white blood cells, red blood cells, and platelets.

White blood cells (WBCs) are part of the body’s immune system. There are several types of white blood cells: neutrophils, monocytes, lymphocytes, eosinophils, and basophils. Each type of white blood cell reacts in a specific way to a threat to the immune system. A CBC counts not only the total number of white blood cells but also each individual type of white blood cell in the blood sample.
Red blood cells (RBCs) are the cells in the blood stream that are responsible for carrying oxygen to the different tissues in the body. A CBC measures the total number of RBCs as well as measuring their capacity to carry oxygen based on hemoglobin levels in the blood. (Hemoglobin is the protein responsible for transporting oxygen.)
Platelets are necessary for blood clotting. Without adequate numbers of platelets, your cat’s blood will not clot properly and your cat will be susceptible to abnormal bleeding. A CBC measures the number of platelets in your cat’s blood.
A CBC also examines the individual cells in your cat’s blood for evidence of structural abnormalities that might be an indication of abnormal function or disease.

A blood chemistry profile measures the various chemical compounds found in your cat’s blood stream. There are several chemicals that are commonly measured.

Blood urea nitrogen and creatinine are measured to evaluate kidney function. They may be elevated due to damage to the kidneys themselves or elevations may indicate other abnormalities in the renal system that impact the kidneys, such as urethral or ureteral obstructions or dehydration.
Chemical compounds used to evaluate liver function include alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and bilirubin. Any or all of these values may be elevated in cases of liver disease, depending on the type of disease. Abnormalities in other organ systems can also cause changes in these values. For instance, adrenal disease can affect some of these values also.
Electrolytes are often included in a blood chemistry profile also. Abnormalities in electrolytes such as calcium, chloride, potassium, sodium, and phosphorus can be associated with many different disease conditions. Abnormalities in kidney function, gastrointestinal disease, seizures, and many other illnesses and/or symptoms can cause or be caused by abnormal electrolyte levels in the blood.
Blood protein levels are also often measured in a chemical analysis. Blood proteins serve many functions in the body. Globulins, a specific type of protein, play a role in immune function. Albumins, another type of protein, help stop fluid from leaking out of the blood vessels and help transport specific molecules to areas where they are required. Other proteins aid in clotting and help regulate gene expression. Typically, a blood chemistry profile will measure total protein levels, globulin levels, and albumin levels.

The measuring of thyroid hormones (usually T4) is performed when thyroid disease is suspected. Hyperthyroidism is a common disease, especially in middle aged and senior cats. It results in elevated thyroid hormone levels circulating in the blood stream.

Testing for feline leukemia and feline AIDS are often part of a basic blood screen as well. These diseases are both caused by retroviruses, although the feline leukemia virus is different from the feline AIDS virus. Testing for these viruses may be recommended if your cat has never been tested before, if your cat has been exposed to another cat that is positive for one of these viruses, if your cat is at high risk of exposure to either virus, or if your cat is ill.

More specialized blood testing may be indicated based on the results of these basic blood tests. However, these are the tests that are most commonly recommended as part of a routine blood screen to evaluate your cat’s overall health.