A question frequently asked during a pet’s annual exam is, “Is the blood work necessary?” Blood work helps us to fully evaluate your pet’s overall health. Changes affecting your pet’s health are not always visible from the outside. The primary goal in an annual examination is to find problems before they become debilitating and, this is where blood work is so important. Realistically, we want the blood work to be normal and, most of the time, it is. However, when it’s not, blood work gives us the clues to find problems.
Of all the blood chemistries, there are certain values that are of greater interest. In a standard panel, we are looking at liver values such as Alkaline Phosphatase (SAP), ALT, Bilirubin and Albumin.
- SAP is the value we most frequently find abnormal. Elevations can have numerous sources including obstruction (partial or complete) of the gall bladder system, bone remodeling as seen in arthritis or severe dental disease, issues involving the adrenal glands which secondarily affect the liver, certain medications such as steroids and other anti-inflammatory drugs, and neoplasia in addition to primary liver disease. An elevated Alkaline Phosphatase is typically seen as a sign to take a closer look.
- ALT is also known as Alamine Aminotransferase or SGPT. Elevations in this enzyme are specific for disease or damage of the liver and like elevations in the SAP. It’s a clue that we need to look further to determine the exact cause of the disease. Frequent causes of elevation in this value include heart disease which results in a decreased blood flow to the liver as well as infections of the liver.
- Bilirubin is a by-product of red blood cell destruction and it is the body’s attempt to recycle hemoglobin in the liver. When the liver is diseased or overburdened by too much red cell destruction, the bilirubin levels go up. There are a multitude of conditions which can lead to this. These include an increase in the number of red cells that are being destroyed and recycled, liver disease, gall bladder disease and certain pancreatic conditions. Most cases of elevation in bilirubin result in a jaundice or yellow- skinned patient and require immediate attention.
- Albumin is the basic protein in our blood. This is produced primarily in the liver. When we have long term liver problems, this decreases. Albumin is also dependent upon the patient’s ability to absorb nutrients from their diet. Animals with GI conditions where nutrition absorption is abnormal can result in low albumin levels.
The next important group of values is an animal’s kidney values. These are primarily blood urea nitrogen (BUN), creatinine and phosphorous.
- BUN is a by-product of protein metabolism which occurs regularly in the animal’s body. This by-product is removed by the kidneys. When those organs are not functioning properly, the BUN becomes elevated. This response is rapid and dramatic to the onset of kidney disease; however, there are other conditions that can result in increases in the BUN as well. These include dehydration and poor kidney blood flow like you would see in heart disease. Elevations in BUN typically result in a sick patient who is lethargic, dehydrated and has had vomiting and diarrhea.
- Creatinine is also a waste product of muscle metabolism that is removed by the kidneys but, unlike BUN, there are few non-kidney conditions that cause it to be elevated. Additionally, an elevated creatinine does not necessarily result in a sick patient. Animals can tolerate elevated levels well; however, when creatinine is elevated it is a reasonably accurate indicator that the disease is in the kidneys.
- Phosphorus regulation also falls in the functions of the kidney and when not functioning properly the levels of phosphorus increase. The levels can increase dramatically with urinary tract obstruction such as stones.
Pancreas related values are also evaluated. These include glucose, amylase and lipase.
- Glucose regulation is a function of insulin production by the pancreas. Insulin allows the glucose or blood sugar to enter the muscles so it can be utilized for energy. When the pancreas is unable to produce enough insulin, this function does not occur and the blood sugar becomes elevated. This elevation overwhelms the kidneys’ ability to reabsorb sugar so the excess sugar comes out in the urine, bringing water with it. This results in an increase in urination. This commonly occurs in diabetic patients.
- Amylase and lipase are pancreatic enzymes that break down starch and fat respectively. When the pancreas is inflamed, these levels become elevated. The same can occur with some types of cancers; however, interpretation of these levels can be difficult and other factors need to be taken into consideration.
A broad category that we regularly monitor is an animal’s electrolytes. These electrolytes include sodium, potassium, chloride and phosphorus. Rather than looking at these values individually, we tend to look at them as a group and how they relate to each other. Areas where we will see abnormalities in the electrolyte values relate to digestion of food. When these values are not “in check”, the patient may have vomiting or diarrhea. At times, this may manifest itself as a disease of the adrenal glands known as Addison’s disease. Significant abnormalities in our electrolyte levels will clue us into the need for further investigation.
The “complete blood count” or CBC includes an evaluation of the white cell (WBC and differential) as well as the red blood cells (PCV or hematocrit and hemoglobin) and platelets.
- WBC/differential is a white blood cell count where specific types of white blood cells are evaluated. Many people assume that an elevation in the white blood cell count is a result of infection. While that is often correct, there are other causes for an increase in the WBC. This is why the differential is important. Inflammation will cause an increase in white cells as the body is attempting to clean up inflammation. Certain parasitic infections will also cause an elevation in particular white cells as will allergic reactions. Dramatic increases can be a result of certain type of blood borne neoplasia. Low white cell counts are seen with immunosuppression which can range from viral infections to neoplasia to side effects from medications.
- Red Blood Count (RBC) evaluation comes in the form of a hematocrit or packed cell volume (PCV) and hemoglobin levels. A low PCV is known as anemia. There are many causes of anemia; like many of the other abnormal results we see in our blood work, a low PCV tells us we need to look further. Common causes of anemia include parasitic infections such as intestinal worms or heart worms, internal bleeding, failure to produce red cells because of bone marrow disease, increase destruction of the RBC, (hemolysis) and kidney disease. An elevated PCV is a result of dehydration. Hemoglobin levels are the oxygen carrying capacity of the blood. Low hemoglobin is typically seen with anemic patients; its causes mirror those that cause anemia.
- Platelets are one of the first lines of defense for bleeding. These cell fragments plug small vessels that are constantly rupturing. The most common cause of low platelet counts is loss from bleeding although there are other conditions that can cause decreased platelet levels. Auto-immune disease as well as the tick transmitted diseases like Lyme Disease or Rocky Mountain Spotted Fever can cause low platelet levels.
Finally, the last component of a Well Pet evaluation is the urinalysis. There is much information to be gathered from such a simple sample. It is not uncommon to find sub-clinical infections in the bladder. These infections can be asymptomatic; yet over a long period of time, can contribute to significant disease such as the formation of bladder stones. Previously we discussed low protein in the blood. One of the more frequent reasons for low protein is loss through the urine. On other occasions, we will find excess sugar in the urine when a patient is diabetic.Crystalsin the urine is a common problem in cats and identifying and preventing them before they collect and form bladder stones can save your cats life.
Lab work gives us additional information about your pet’s health than cannot be obtained in any other way. It provides your veterinarian with the ability to identify a problem before it becomes an emergency.