Poor Abby was clearly in distress. For the past several weeks, the eight-year-old Persian had shown little interest in her food – the same food shed been eating quite enthusiastically all of her life. When she did eat, she would spit up her food soon afterward. She also seemed to be incessantly thirsty, lapping up great quantities of water and urinating every half-hour or so.
Fortunately, Abby was due for her annual veterinary checkup, during which she would undergo a series of blood tests, one of which – called a chemistry panel – would meticulously measure the levels of various chemical substances in the animals blood.
Solving the Mystery
At the clinic, the chemistry panel findings convincingly supported what the veterinarian suspected after reviewing Abbys medical history and performing a thorough physical exam. The test revealed abnormally high blood levels of two substances – blood urea nitrogen (BUN) and creatinine – which indicated that her kidneys were not adequately filtering her systems metabolic wastes. Subsequent ultrasound imaging confirmed beyond a doubt the veterinarians tentative diagnosis of early-stage renal failure.
Luckily, though, the blood test identified the condition before Abbys kidneys had sustained severe damage. She was put on a new diet, specifically designed for cats with kidney failure. Within a few weeks, the dramatic signs of kidney failure had subsided, and her veterinarian was confident that, with ongoing supportive care, her condition could be kept stable.
A Wise Investment
Routine bloodwork like the battery of tests that probably saved Abbys life is what Richard Goldstein, DVM, calls our first tier of defense – after thorough physical examination – against life-threatening feline diseases. In his view, all geriatric cats (those eight years of age or older) should undergo these screenings annually. The second tier of defense, he notes, involves specialized tests in which an animals blood is examined for specific signs of suspected organ malfunction or the presence of specific infectious agents.
A routine test can cost an owner about $100, says Dr. Goldstein, who is an assistant professor of small animal medicine at Cornell Universitys College of Veterinary Medicine. But its money well spent, he observes. Its better financially to spot a health problem early and to prevent it from getting worse than it is to try to deal with it after it has progressed.
As with human blood, the chief function of feline blood is to carry oxygen and nutrients to the bodys tissues and to transport carbon dioxide and wastes away from them. It also serves in such processes as cell development, tissue repair and the warding off of infection.
Also like human blood, feline blood is made up of red cells (erythrocytes); white blood cells (leukocytes); platelets; and a colorless fluid (plasma) in which these and other life-supporting blood components – such as hormones, proteins and salts – are suspended. All of these ingredients in their proper balance are vitally important to a cats health, and routine bloodwork evaluates them in two processes: (1) a complete blood count (CBC) and (2) the chemistry panel.
The Usefulness of the CBC
Using about one-twentieth of an ounce of an animals blood, the CBC (also known as a hemogram) includes the following major measurements and evaluations:
A packed cell volume (hematocrit) reveals the concentration of red blood cells in the plasma. A low red cell concentration might indicate that the animal is anemic – either its bone marrow isnt producing the cells in sufficient number or they are being lost or destroyed. A high concentration could mean that it is dehydrated.
A red blood cell count measures the actual number of red cells in a given amount of blood and discerns any abnormalities in their shape, size or color. The amount of hemoglobin – a substance that transports oxygen throughout the bloodstream – is also assessed.
A white blood cell count evaluates and counts the number of leukocytes (including lymphocytes, neutrophils, monocytes, eosinophils and basophils, which play various roles in attacking and destroying disease-causing organisms), that are being produced in the bone marrow or other tissues. A high white cell count may indicate, for example, that an animal is harboring an infection, is under extraordinary stress or is affected by a serious and chronic illness, such as leukemia.
A platelet count measures the concentration of disk-shaped blood cells (thrombocytes) that promote vitally necessary blood clotting.
The CBC also measures the protein levels in blood plasma. Low levels of these proteins suggest, for example, the possibility of liver, kidney or gastrointestinal malfunction, while high levels indicate the presence of infection, chronic inflammation or some types of cancer.
The Chemistry Panel
The chemistry panel focuses on the chemical components suspended in the clear, watery content (serum) of the blood after it has been separated from the cells and from certain proteins that are needed for clotting.
In these tests, levels of a dozen or more substances – in addition to creatinine and BUN – are evaluated in order to assess a wide range of health-determining factors. The chemistry panel can reveal problems in an animals organ function. It can measure the levels of necessary hormones. And it can determine whether the blood is sufficiently rich in electrolytes – chemical compounds that regulate the exchange of necessary electrical charges across cell membranes.
Abnormal (or subnormal) blood levels of various substances may indicate damage or disease involving the kidneys, liver, muscles, or glands. For example:
High levels of alkaline phosphatase may indicate liver damage.
Elevated amounts of amylase may indicate kidney or pancreatic disease.
Abnormal calcium levels may indicate the presence of tumors, kidney disease or other disorders.
High levels of blood sugar (glucose) may indicate diabetes.
Low levels of potassium may explain an animals chronic lethargy or lack of muscle control.
In addition, a chemistry panel measures total protein, including one protein called albumin and others known as globulins. High or low blood levels of these proteins can influence many bodily processes, including the ability to retain water and to defend against infection.
The value of basic bloodwork is indisputable and – along with patient history, thorough physical exam and urinalysis – is well established as a fundamental element of modern veterinary practice, says Dr. Goldstein. Most veterinarians, he says, will start with the basic screen because the procedure is noninvasive and provides so much information.
The use of blood testing, however, is not limited to routine preventive medicine. Animals who are about to undergo serious surgery, for example, will almost always have a CBC and chemistry panel done beforehand to make sure that they can tolerate anesthesia. And blood serum tests have been developed to help identify substances that produce allergic reactions in animals.
In some cases, however, the results of a CBC or blood chemistry panel may be confusing or not readily explicable. Or the routine tests may be inappropriate for a specific purpose, such as targeting a certain organ or testing for infection with FIV (feline immunodeficiency virus), FeLV (feline leukemia virus), or some other disease agent.
But even specific tests that go beyond the CBC and chemistry panel, says Dr. Goldstein, tend to be relatively inexpensive and can often be performed by a technician in a veterinary clinic.
Results of routine bloodwork and most specific blood tests, he notes, can be available almost immediately. On the other hand, he points out, some tests are more complex and rigorous and will require blood samples to be shipped to a specialized lab. For example, he notes, a test for endocrine function may have to be sent far away, and the results may not come back for days or weeks.
If a specific blood test confirms the suspicions raised by the CBC or chemistry panel, says Dr. Goldstein, diagnostic efforts are likely to move to the third tier of defense, which will rely heavily on imaging techniques such as X-rays and ultrasound – “techniques that can pick up things that cant be revealed in a blood test.