Lab tests are being run. Image ourtesy of CDC.
Because normal laboratory values depend on the diagnostic method used, the normal variation in species/breed/age test results, and so on, we won't provide a numerical listing of values here. For example, a normal CBC for a pediatric kitten varies from that of a geriatric dog, and a healthy Greyhound's values may differ from those of a healthy German Shepherd dog. In addition, numbers have to be interpreted as a whole; individual abnormalities do not provide a meaningful look at overall health. (And laboratory errors do exist, so focusing on one oddity may lead to owner stress.)
Lab results can be affected by the medications your pet is taking and by the timing of the test in relation to food ingestion, so always ask if your pet should eat or take his normal medication before running the test. (It's just like when you have to have blood work done; your physician requires some tests to be done in a fasting state and some not.)
The normal range of values from a given test at a given laboratory will usually be listed on the results form so that you can see immediately what is not in a normal range; often, results considered to be outside of the norm will be in bold text. Your veterinarian will point out to you which values are of concern and why. Because of the complexity and interrelationship of these values, allow your veterinarian to interpret them for you. Guessing a worst-case scenario will just cause you preventable stress. Sometimes the tests will need to be repeated.
Complete Blood Count (CBC)
A CBC measures the number of red blood cells, white blood cells, and platelets. Red blood cells carry oxygen. The CBC also measures hemoglobin, which is the part of the red blood cell that carries oxygen. Most white blood cells fight infection; if an animal has a high white cell count, the pet may have an infection. The platelet count is important because platelets help make blood clot properly.
Alkaline phosphatase forms in body tissue. Increased levels in dogs typically indicate liver or bone disease, or that the dog is taking prednisone. Liver and bone disease are the most common causes for increased values in cats.
ALT is an enzyme produced in the liver, and values found in the bloodstream increase with a diseased or damaged liver.
Amylase and Lipase
Amylase is an enzyme that is produced by the pancreas and the intestinal tract. It helps break down sugar. Lipase is an enzyme that helps break down fats. Pancreatitis or cancer of the liver can raise the value of both of these enzymes.
Bile acids help break down fat. Because these acids are produced in the liver, a bile acid test evaluates both the liver itself and the blood flow to it. Typically, bile acid tests are run pre-prandially (before eating), and post-prandially (two hours after eating).
In the liver, bilirubin is created from old red blood cells. It leaves the body in urine and stool. Values can be elevated in pets with liver or gallbladder disease, or in those animals whose red blood cells are being destroyed faster than normal. Pets with elevated bilirubin can appear jaundiced (abnormal yellow skin color).
Blood Urea Nitrogen (BUN)
BUN is a waste product. A low BUN can indicate liver disease, and an increased BUN can indicate severe kidney disease or dehydration.
Typically, high blood calcium is associated with cancer, but there are other causes, such as kidney failure, bone disease, or poisoning from rodent bait. Low blood calcium can occur just before giving birth or even during nursing (eclampsia), problems with the parathyroid gland, or poisoning from antifreeze.
As it is in people, cholesterol is a fat. Unlike in people, it doesn't contribute to heart disease in dogs and cats. Increased cholesterol is less common in cats than in dogs. Several diseases (diabetes, hypothyroidism, Cushing’s, or kidney disease) can elevate cholesterol levels.
Creatinine is produced in the muscles and leaves the body in the urine. Elevated values indicate kidney disease or dehydration.
Creatinine Kinase (CK)
Damaged muscles produce creatinine kinase, which goes into the bloodstream. High values indicate problems with muscle, possibly including the heart.
Diabetes is a typical cause of elevated glucose, which is blood sugar. Dogs with Cushing’s disease may also have elevated levels. If the glucose has been high for a while, it can be found both in the blood and urine. Low glucose levels may indicate a body-wide bacterial infection (sepsis) or pancreatic cancer; seizures are sometimes seen with low glucose.
Phosphorus may be high in pets that have chronic, serious kidney disease.
Acute kidney failure can increase levels of potassium in the bloodstream.
Proteins (Albumin, Globulin)
Albumin is a protein created in the liver. It transports hormones, enzymes, medications, etc., through the body and helps to keep fluid from leaking out of the bloodstream. Abnormally low ranges are seen with diseased livers, gastrointestinal disease, etc. Over 60 - 80% of the liver must be destroyed before albumin decreases significantly. Because albumin has a long half-life of seven to ten days, it is not usually affected by acute liver disease.
If only total protein (TP) is measured, hypoproteinemia (low protein levels) associated with liver disease may be missed because globulin levels (proteins in the blood) may be elevated with certain liver diseases. Albumin levels must be interpreted while also considering globulin levels and clinical signs. Decreased albumin with normal globulin levels implies reduced production in the liver or increased loss (for example, hemorrhage). A combined decrease in both albumin and globulin usually means bleeding or dilution. Inflammatory conditions can temporarily reduce albumin production.
The only time albumin is increased is when the animal is dehydrated. Albumin helps keep plasma (the liquid part of the blood) from migrating out of the blood vessels and into the surrounding tissues, which would cause edema and other problems.
Hyperglobulinemia (elevated globulin levels) can result from neoplasia (lymphoma, leukemia, multiple myeloma, or carcinoma) or infectious/inflammatory/immune-mediated diseases. (A serum protein electrophoresis may help determine the cause of hyperglobulinemia.)
Symmetric dimethylarginine (SDMA) is excreted primarily by the kidneys. The serum concentration of SDMA is affected by changes in the glomerular filtration rate (GFR). SDMA has been shown to be a more sensitive biomarker than serum creatinine for assessing renal dysfunction in people. Studies have shown that SDMA increases after 40 percent of kidney function is lost, and creatinine increases after 75 percent is lost. Many things can affect the SDMA numbers, so an increase in the SDMA number should be interpreted appropriately. Things that can affect the number are hydration status (dehydration, water restriction for surgery, etc.), age of the animal (young animals tend to have higher numbers than adults), medications (e.g., NSAIDs), post-renal obstruction, low blood pressure, infections, thyroid disease, etc. (Anything that decreases the kidneys' ability to filter the blood will cause an increase in the SDMA number.)
Low sodium levels are commonly seen in Addison’s disease. Dehydration can cause slightly elevated levels of sodium.
Total protein is a value that includes albumin plus larger proteins (globulins). Total protein can be increased from dehydration or activity of the immune system; like albumin, values can decrease due to liver disease.
While we sometimes think of it just for urinary tract infections, urine tests can provide diagnostic information about a number of diseases. How urine is collected for this test may depend on what disease is suspected. Urine can be caught in a cup during urination or by placing a needle directly into the bladder (cystocentesis, which isn't as bad as it sounds), or even with a catheter.
Sometimes, lab results are faulty. If you find several elevated or decreased values, but your pet acts as though illness is not an issue, there could be problems with the tests, and they may need to be repeated – after all, who are you most likely to believe, a dog who is running around normally and thinks he’s healthy or scary lab numbers? If your pet acts normal but the values are odd, it's usually better to repeat the tests and eliminate all doubt about the results than to medicate a healthy animal.