Bloodwork before surgery: is it really necessary for your pet?

A common question asked by many pet owners prior to surgery is “why do we have to do the bloodwork?” At Maricopa Animal Hospital we often hear comments such as “my pet is young he/she doesn’t have any problems” or “you did an exam on my pet and said he/she is healthy.”

There are many reasons that bloodwork is done before any surgery is performed. It provides us with a glimpse of what is going on inside the body. Even though a pet may appear healthy on the outside, it doesn’t always mean there’s not something more going on inside. To obtain a better understanding of why the bloodwork is done, this article will look at each item that is evaluated and discuss some of the reasons why we might have concerns for abnormalities.

There are two main tests that are performed prior to routine surgeries. If there are abnormalities on these tests, further testing may need to be done to find a more specific diagnosis. These other diagnostic tests will not be discussed in this article.

The first test performed is a Complete Blood Count. This test deals with the cell portion of the blood. Several things are measured with this test:

1. Hematocrit: it measures the percentage of red blood cells in the blood. This helps to determine if your pet is dehydrated or anemic. There are many possible causes for abnormal findings in the hematocrit (ranging from internal parasites to immune mediated problems), and further evaluation would be recommended if your pet was significantly dehydrated or anemic.
2. Hemoglobin: it is the oxygen carrying pigment of red blood cells. Typically this value follows changes in hematocrit and red blood cells when there is anemia present.
3. Red Blood Cells: these cells carry hemoglobin, which transports oxygen to the tissues and carries carbon dioxide to the lung for removal. Decreases in red blood cell levels are indicators of anemia, which could suggest underlying toxicities, diseases found from ticks, or certain viral diseases.
4. White Blood Cells: these are the immune cells of the body. There are five different types of white blood cells: neutrophils, basophils, lymphocytes, monocytes, and eosinophils. Each of these cells works in different ways to complete the inflammatory process when there is an abnormality in the body. Often elevation in white blood cells is an indicator of stress or infection. Changes in these cells can also point to lymphoma or viral infections.
5. Platelets: these work together to form a plug anywhere that there is damage to a vessel. Essentially they help to form a clot. If these levels are decreased there are concerns for possible viral, tick-borne diseases, immune mediated diseases, etc. If a pet that had a very low platelet count were to be placed under anesthesia and surgery performed, there is a high potential that the blood will not clot correctly and the pet may lose too much blood.

A Serum Chemistry is the second test performed prior to surgery. It handles the fluid portion of blood (the serum). The following are the major enzymes measured:

1. ALT (Alanine Transferase): This enzyme is produced in the liver. It is the most sensitive indicator of active liver damage. When we see elevations in this enzyme, we know something abnormal is occurring in the liver. Unfortunately, we don’t know the cause of the increase with this test alone. Often further testing is required to help distinguish between something as simple as an infection to something more significant such as a portosystemic shunt or cancer. It is not uncommon to find abnormalities in this enzyme even in young pets.
2. Alkp (Alkaline Phosphatase): This enzyme is found in the liver and bone. Elevations in it can point to several things, including active bone growth in puppies, liver damage, Cushing’s disease (adrenal gland problems), chronic stress, and hyperthyroidism in cats.
3. AST (Aspartate Transferase): The liver, muscle and red blood cells are all places this enzyme can be found. Increases in it can be related to liver disease, heart disease or skeletal muscle trauma.
4. BUN (Blood Urea Nitrogen): This enzyme is made by the liver and excreted in the urine. Elevations in it can be an indicator of many things: dehydration, kidney failure, urinary obstruction, fever, trauma, gastrointestinal upset and heart disease. Low levels of it can indicate liver disease or anorexia (particularly a low protein diet).
5. Creatinine: This enzyme is a breakdown product of muscle creatine. It is excreted in the kidney. Increases in this enzyme signify kidney problems. Decreases may suggest muscle wasting.
6. Amylase: It is made in the pancreas and is excreted by the kidneys. It can point to inflammation of the pancreas, kidney insufficiency, or gastrointestinal disease.
7. Albumin: This is a protein in the serum that is produced in the liver and lost by the gastrointestinal tract or the kidneys. Increases in this enzyme denote dehydration. Decreases can reveal liver disease, blood loss, gastrointestinal disease or kidney disease.
8. Total Protein: Increases in total protein can designate dehydration or chronic immune stimulation. Decreases lead us to think of possible protein losing intestinal diseases, hemorrhage, liver disease, cancer or malnutrition.
9. Globulin: This is a protein that’s involved in the immune defense system. In Arizona we often find increases in this level with diseases such as Valley Fever and Tick Fever. It can also be indicative of lymphoma, infectious peritonitis, or other immune stimulating diseases. Blood loss or protein losing intestinal diseases can lead to decreases in the protein.
10. Cholesterol: The liver produces cholesterol, and it is absorbed by the intestines. Increases suggest hypothyroidism, Cushing’s disease, diabetes, or a high fat diet. Decreases can be related to liver failure or gastrointestinal problems.
11. Glucose: This measures blood sugar levels. High glucose levels can be caused by stress, diabetes or Cushing’s disease. Low levels are often associated in small breed dogs that are not getting enough nutrients. Other possible low causes can be end stage liver disease, sepsis, or certain cancers.
12. Phosphorus: Increases in this enzyme can be normal in young animals. Other potential causes of increase could be kidney disease, hyperthyroidism, or bleeding disorders.
13. Calcium: Elevated levels point to tumors, hyperparathyroidism, kidney disease, or possible toxicity. Low levels can be related to pregnancy, kidney disease, malabsorption, or pancreatitis.

As you can see, there are a wide variety of things that your veterinarian looks for and evaluates on the bloodwork done prior to surgery.

It is important to remember that this list is by no means comprehensive of all the diagnostics or blood tests out there, but these are the basics done prior to routine surgery. Often times an abnormality found on the bloodwork has to be evaluated by your veterinarian along with physical history, exam and possible other diagnostics to come to a specific reason for an elevation or decrease in that enzyme.

For further information contact Dr. Kelly Anderson via the clinic’s Web site or at (520) 568-2224.

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