Understanding bloodwork for your pet

At The Pet Doctor, we often recommend bloodwork as a valuable diagnostic tool.  Bloodwork gives us an idea about a lot of things that can be going on with your pet. 

The doctors at The Pet Doctor will interpret these laboratory tests in light of the entire examination of your pet. Sometimes laboratory tests need to be repeated to evaluate trends, which may provide more information than measurement of a single test. 

We are always happy to discuss bloodwork and other lab results.  We can then work together to develop a treatment plan for your pet.

The following is an explanation of some of the things that can be diagnosed with routine bloodwork:  

Complete blood count (CBC)
The complete blood count is the number of red and white blood cells circulating in the bloodstream.  Red blood cells are produced in the bone marrow and are used to deliver oxygen throughout the cells of the body. New red cells are made all the time and the number of new cells can tell us about the regeration capacity of the bone marrow.  Damaged or old red blood cells are removed from the blood by the spleen and liver. Red blood cell numbers can be decreased (anemia) if they are not produced in adequate numbers by the bone marrow, if the pet’s body is destroying them (hemolysis), or if they are lost due to bleeding.  We can also determine dehydration status by the red blood cell count.  This is important to help us to evaluate a need for fluid therapy. 

White blood cells are used by the immune system to fight infection.  There are several types of white blood cells in blood. Lymphocytes are produced in lymph nodes throughout the body. The other white blood cell types are produced in the bone marrow along with the red blood cells and platelets. The majority of white blood cells in circulation are neutrophils, which help the animal fight infections. Neutrophils can be decreased in pets with bone marrow disease, in some viral diseases, and in some pets receiving cancer chemotherapy drugs. Neutrophils are increased in pets with inflammation or infection. Lymphocytes may be increased with an infection, they can be decreased in pets who are severely stressed. Certain drugs, such as steroids will decrease the number of lymphocytes. Eosinophils and basophils are increased in pets with allergic diseases, or parasitic infections.
Platelets are produced in the bone marrow and are involved in blood clotting and stopping bleeding. Platelets live a few weeks and are constantly being produced by the bone marrow. Low platelet counts occur if the bone marrow isn’t producing them, or if the platelets are destroyed at a faster rate than normal. Animals with a low platelet count bruise easily and may have blood in their urine or stool.  This can be very dangerous if platelet numbers get to a very low level.

The serum chemistry panel gives us an overview of the health, and sometimes the function, of body organs. Some blood tests are very specific for a single organ, whereas other tests give us information on several organs.  Our routine chemistry panel includes the following tests:

Albumin is a protein produced by the liver. Albumin is decreased if the liver is damaged and cannot produce an adequate amount of albumin or if albumin is lost through damaged intestine through diarrhea or in the urine due to kidney disease. The only cause of increased albumin is dehydration.

Alkaline phosphatase originates from many tissues in the body. When ALP is increased in the bloodstream of a pet the most common causes are liver disease, bone disease or steroids.  The steroid can be due to a drug that has been given or due to increases in the body’s production of adrenal hormones. 

ALT is an enzyme produced by liver cells. Damage to cells in the liver causes an elevation of this enzyme in the blood.

Amylase is an enzyme produced by the pancreas and the intestinal tract.  Amylase may be increased due to pancreatitis (inflammation of the pancreas). 

Lipase is another pancreatic enzyme which is responsible for the breakdown of fats and which may be increased in patients with pancreatic inflammation or cancer.  We also have a Canine Pancreatic Lipase which is an even more specific test to help confirm the diagnosis of pancreatitis.

Bilirubin is produced by the liver from the breakdown of old red blood cells. Bilirubin is further broken down and eliminated in both the urine and stool. Bilirubin is increased with some types of liver disease, gallbladder disease or in patients who are destroying their red blood cells (hemolysis).   Increases in bilirubin can also cause jaundice or icterus.  Icterus is most easily seen as a yellowing around the white part of the eye, inside the ears and on the gums.

Blood urea nitrogen is influenced by the liver, kidneys, and by dehydration. Blood urea nitrogen is a waste product produced by the liver from proteins from the diet, and is eliminated from the body by the kidneys. A low BUN can be seen with liver disease and an increased BUN is seen in pets with kidney disease. An elevation is also seen with dehydration.  The kidneys must be damaged to the point that 75% of the kidneys function is lost before BUN will increase.   Until treatment is given, we will not know if the cell damage is permanent or reversible. 

Calcium in the bloodstream originates from the bones. High blood calcium is most commonly associated with cancer. Less common causes of elevated calcium are chronic kidney failure, over-function of the parathyroid gland, poisoning with certain types of rodent bait and bone disease. 

Cholesterol is a form of fat. Cholesterol can be increased in the bloodstream for many reasons in dogs. It is much less common for cats to have increased cholesterol. High cholesterol does not predispose pets to heart disease as it does in people.

Creatinine is a waste product that originates from muscles and is eliminated from the body by the kidneys. An elevation of creatinine is due to kidney disease or dehydration.  It does not change as quickly as BUN and may be a more reliable indicator to monitor kidney disease long term.

Glucose is blood sugar. Glucose is increased in dogs and cats with diabetes. It can be transiently elevated in cats due to the stress of being at the vet hospital. 
Low blood sugar occurs less commonly and can be a sign of cancer or sepsis.  It is often seen in young puppies or kittens before they are able to regulate their blood sugar well. Low blood sugar can cause depression or seizures.

Phosphorus in the bloodstream originates from bones. Phosphorus is increased in the bloodstream in patients with chronic kidney disease. Like BUN and creatinine, phosphorus increases in these patients when about 75 function is lost

Potassium is increased in the bloodstream in the pet with acute kidney failure such as kidney failure caused by antifreeze poisoning, in dogs with Addison’s disease and in animals with an obstructed bladder. 

Potassium is lost from the body in vomit, diarrhea and urine. Low blood potassium can cause the pet to feel weak. Cats with low potassium may have muscle abnormalities.

Sodium may be increased if the patient is dehydrated. Low blood sodium is commonly seen with Addison’s disease (hypoadrenocorticism).

Total protein includes albumin and larger proteins called globulins. Globulins include antibodies used by the immune system to fight disease. Total protein can be elevated if the pet is dehydrated or if the pet’s immune system is making large amounts of antibody. Total protein is decreased in the same situations which reduce albumin or if the pet has an abnormal immune system and cannot produce antibodies.