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by Maren Bell Jones DVM, MA, June 9, 2014
"I'd like to do some bloodwork."
You might have heard another veterinarian or myself say this after doing a thorough physical exam on your pet and wondered why would we make this recommendation. What we are looking for? What exactly is "bloodwork" and what do all those numbers mean?
In dealing with sick animals, we don't have the benefit of asking specifically how they feel. They can't tell us they feel a little light headed, have a headache, or are a little queasy. They can't tell us they feel tingling down their left rear leg from the disc compression in their spine. They can't tell us that their abdomen hurts from an inflamed pancreas, a blocked gall bladder, or they have a urinary tract infection. We have to go by what you report as the owner and what we as the doctor sees. This is one of the top reasons we request to bloodwork in your pet is because they are showing signs of illness and bloodwork can tell us why and how severely. When different processes in the body are off because of disease or other problems, they often but not always appear when we do bloodwork.
Besides figuring out what disease an animal has, what are some other reasons that I often do bloodwork? I see many older dogs for mobility issues. Since big dogs in particular can go down and not get back up, this is consistently cited as a reason for an owner deciding on euthanasia in an older, large breed dog. I really try to encorporate a combination of holistic and conventional medications and strategies to manage the arthritis and pain that comes from degenerative joint disease. This includes the use of NSAIDs (non-steroidal anti-inflammatories) like meloxicam. Just as in people, dogs can have some of the same side effects to NSAIDs as people can: GI upset, GI ulcers, and liver and kidney dysfunction. NSAIDs are sometimes near miraculous in how much they help arthritic pets, but they must be used judiciously and at the lowest dose possible to be effective. As your own physician would, I do a complete blood count (CBC), chemistry panel, and urinalysis (UA) before starting long term NSAIDs to make sure there are no signs of anemia, the liver and kidney values are appropriate, and there are no signs of kidney disease on the urinalysis. We do a quick recheck every 6 months to make sure they are still doing well.
So when we talk about doing "bloodwork," what does that mean exactly? It depends on what we are looking for. In general, I start with what is called a CBC/chemistry/UA. These tests are run partially on very sensitive and specialized machines and partially by the veterinarian or a laboratory technician looking at the blood or urine under the microscope. The CBC tells me about the type of blood cells the animal has in their body (red blood cells are responsible for transporting oxygen, white cells are the soldiers in the army of the immune system, and platelets are for clotting if we get hurt or injured). I look for conditions like anemia (low red blood cell count), elevated white cell count (common in infection or inflammation), low platelets, and if there are any abnormal cells or even blood parasites floating around in circulation.
The next thing we look at is a chemistry panel. We are looking at blood glucose (blood sugar), kidney values like blood urea nitrogen and creatinine, liver values like cholesterol, bilirubin, and the liver enzymes, and the electrolytes such as sodium, potassium, and calcium. These numbers can get very complicated very quickly sometimes. In certain disease states, some or all of these can be "off," though in some cases, this is not necessarily always a dire situation. There is individual variation within different patients. However, we put these values together like pieces in a puzzle to get an overall picture. One thing to keep in mind is that just because the blood work is totally within normal limits does not mean that the organs are all 100% okay. The liver sometimes has to be damaged by up to 75% before it starts showing signs on the bloodwork. The kidney may have only one third of its cells working properly before it shows up on the bloodwork. We use the overall picture of how the animal is doing and treat the patient, not the numbers.
The last component is the urinalysis. We look at the specific gravity to see how well the kidney can concentrate urine as one of its main jobs as well as looking for the presence of red blood cells (blood in the urine), white blood cells (possible infection), abnormal cells or levels of protein, glucose, or ketones, which can signal kidney damage or diabetes. Bacteria can sometimes be seen in order to diagnose a suspected urinary tract infection. However, for difficult UTIs, culturing the bacteria on a petri dish and seeing what antibiotic the bacteria are sensitive to is often more diagnostic to help solve the problem.
Bloodwork interpretation is one of the most common diagnostic tools and yet one of the most challenging aspects of medicine. The values are dynamic and change day by day or even hour by hour! This is why bloodwork from six months ago is not valid for what is happening in the body today. In addition, the values themselves don't often point to just one single disease. Usually a number that is high or low can be caused by a myriad of conditions, which is why interpreting the results is difficult. The tendency by owners is to sometimes self research those numbers and put together their own picture. While this is a natural inclination, it is not usually quite that simple. Often a CBC/chemistry/UA has to be followed by additional diagnostics for other blood tests (thyroid hormone testing, bile acids for the liver, and so on) or advanced imaging such as radiographs (x-rays) or ultrasound. I will go through each finding with you and explain why I came to the answer (or the need to find more answers!) as we get the results. If you ever have questions, please don't hesitate to ask!