Laboratory Tests Routinely Performed in Veterinary Medicine
Some of the most common basic tests performed by a veterinarian, veterinary technician, or laboratory personnel are discussed below. Tests may be performed at your veterinarian’s clinic, or samples may be sent out to a laboratory.
Just as your physician will check your vital signs, weight, and other conditions when you visit the doctor, your veterinarian will also want to check vital signs, perform a physical examination, and obtain basic medical information about your pet. In addition to checking your pet’s weight, looking at your pet’s eyes, checking its ears, examining the mouth and teeth, and observing the pet’s movements, there are other simple tests that are often performed.
The veterinarian will use a stethoscope to listen for heart, lung, and digestive system sounds that may indicate whether there are problems with these organs.
The veterinarian may gently press on the pet’s gums with a finger and then release the pressure to determine how long it takes for the capillaries in the gums to refill. A longer than normal capillary refill time may indicate that the pet's circulation is poor and could be going into, or be in shock. Longer refill times also occur in certain heart diseases. The color of the gums can also indicate problems such as jaundice (a sign of liver disease), shock, or anemia.
Veterinarians use abdominal palpation to check for the size and location of internal organs such as the liver, spleen, kidneys, and urinary bladder. They will also check for enlargement of lymph nodes located throughout the body.
If your pet has a specific problem at the time of the examination, the veterinarian may perform additional tests that are not generally part of a routine physical examination. For example, examination of a dog with suspected vision problems might include tests that assess overall vision, examination with an ophthalmoscope (an instrument that allows the veterinarian to see the interior portions of the eye) and various stains, and determination of the pressure within the eye (intraocular pressure). Similarly, examination of a lame horse might include a hands-on examination of the affected leg, blood and biochemical tests, muscle biopsy, and various types of imaging techniques.
Most veterinary clinics can perform basic laboratory tests within their clinic. Samples for the tests may be collected at the clinic, or the pet owner may collect samples at home (feces, urine) and bring them to the clinic. The complexity and types of tests done will vary from clinic to clinic. The following types of tests are frequently done at an in-house laboratory.
Many tests can be run on blood samples, but only a limited number are typically carried out at veterinary clinics. As tests become more automated, some veterinarians are able to offer a wider range of tests at their own clinic, but the majority are still done by outside laboratories (see below).
One of the most common tests is a complete blood count (CBC) that analyzes the numbers and appearance of blood cells. The CBC is important in the diagnosis and monitoring of disease and infection. Blood samples are usually taken by the veterinarian or a veterinary technician for analysis. There are three main parts of the CBC dedicated to providing information about red blood cells, white blood cells, and platelets.
There are three common measurements made using red blood cells: packed cell volume, hemoglobin concentration, and red blood cell count. All three are interrelated and help your veterinarian diagnose diseases. The packed cell volume is the proportion of the whole volume of blood occupied by the red blood cells. When the proportion of red blood cells is high, the condition is called polycythemia. Polycythemia is common when a pet has dehydration or diarrhea. A low packed cell volume may suggest anemia or bleeding. The hemoglobin concentration in the blood sample indicates the oxygen-carrying capacity of the red blood cells. The red blood cell count is the number of red blood cells in a unit volume of blood. The results of the tests on red blood cells can tell your veterinarian a lot about the way your pet’s body is functioning and suggest possible health problems.
There are two main types of white blood cells, phagocytes and lymphocytes.
Phagocytes are cells that can surround and consume foreign particles, cellular waste, and bacteria in the blood or in tissues and are classified as either granulocytes or mononuclear cells. Granulocytes protect against bacteria, fungi, and parasites and may be involved in allergic reactions. Neutrophils are the most common type of granulocytic white blood cell and are the first line of defense against bacterial invasion. They increase in number during inflammation, infection, and short-term stress. Eosinophil numbers go up during allergic reactions, and in response to certain tumors and parasites. Basophils are the least common type of white blood cell and increase with inflammation. Monocytes are large cells with a single nucleus that increase in number during chronic diseases. Their main function is to migrate to damaged tissue, where they are called macrophages, and clean up debris.
Lymphocytes are the white blood cells responsible for antibody production and cell-mediated immune responses. Large increases in the number of lymphocytes often indicates leukemia, a type of cancer.
Platelets are cell-like particles in the blood. Another name for platelets is thrombocytes. Platelets are much smaller than red or white blood cells. They perform a critical role in the clotting process to repair damaged blood vessels. Thus, injuries often prompt a large increase in number of platelets. Some autoimmune diseases, blood clotting disorders, and bone marrow problems cause a decrease in the number of platelets.
Stool samples may be collected by the pet owner before an appointment or they may be collected by the veterinarian. A small amount of the stool sample may be directly applied to a glass slide or first processed within a fluid. The material is then examined under a microscope. The purpose of using certain fluids before stool examination is to detect the presence of the cysts of parasites such as Giardia and Cryptosporidium or eggs of other parasites, such as roundworms, hookworms, and tapeworms. Larva, adult worms, or tapeworm segments may also be observed.
Analysis of urine samples (urinalysis) is important for detecting various types of urinary tract diseases. The sample should be analyzed immediately after collection or be refrigerated and transported to the laboratory as soon as possible after collection. Urine left at room or higher temperature will degrade, and test results will not be accurate. Also, urine samples should not be frozen, because freezing will change several important characteristics of the urine. The tests usually carried out on urine samples include evaluating the appearance, chemistry, and sediment.
Normal urine is yellow or amber in color and should be transparent or clear. The presence of diseases or infections may change the color or clarity. For most pet species, normal urine has a slight odor of ammonia; however, the urine of some pets (such as cats) normally has a pungent odor. A bacterial infection of the urinary tract may produce a strong ammonia odor in the urine.
Chemical analysis of urine includes determining its specific gravity (density), pH (degree of acidity or alkalinity), amounts of protein, glucose, fragmented blood cells, and more. Changes in any of these may indicate disease, injury, or defects. Microscopic examination of urine sediment (the solid part of urine obtained by spinning the urine sample in a centrifuge) is part of a routine urinalysis. Large numbers of red blood cells in urine sediment usually indicate bleeding somewhere in the urinary tract, whereas large numbers of white blood cells usually indicate an infection. Other solid components of urine, known as casts, are tubular structures formed in the kidneys. Increased numbers of casts may indicate kidney disease. Crystals may be present in low numbers, and some types are not considered to be a problem. Bacteria may be present in small numbers in normally voided urine, but large numbers indicate infection. If your veterinarian suspects a bladder infection, a sample of urine to culture for bacteria may be collected directly from the bladder using a needle and syringe. This process is called cystocentesis.
Many of the tests the veterinarian uses to diagnose disease require either specialized equipment or training of technicians performing the tests. For these reasons, many veterinarians send the samples to an outside laboratory. Some tests are similar to those available in the clinic, but advanced testing equipment and quality control procedures in a specialized facility may offer advantages in speed and accuracy. For example, the specialized laboratory, will usually have staff pathologists to identify abnormal red or white blood cells, both of which can help confirm a disease diagnosis, during routine tests on a blood sample.
In addition, at an outside laboratory specialized tests may be performed, such as one to detect larval stages of parasites that are not easily found on standard tests. Because parasites also occur in samples other than stool samples, a direct smear of a pet’s blood on a slide can be analyzed to detect the presence of blood parasites.
Most laboratories offer a basic group of tests, known as a basic chemistry test panel, which provides information regarding many general health problems (see Table: Tests Included in a Basic Test Panel). Having a laboratory perform these tests can help point to a diagnosis, particularly if the animal has vague signs and a history that make it difficult to determine the problem. The basic group of blood tests for pets includes total protein, albumin, globulin, urea, creatinine, alanine amino transferase (ALT), and alkaline phosphatase (ALP). The results of these tests provide information about hydration status, inflammation, some heart diseases, kidney and liver function, and blood sugar levels. This group of tests may be modified as appropriate for other animals. Based on the results of this group of tests, other tests may be carried out as needed to reach a definite diagnosis.
Tests Included in a Basic Test Panel
When pets have an infection, it is important to identify the specific bacteria or other organism that is the cause so that your veterinarian can prescribe a proper treatment program. Although many microbiology tests can be performed at veterinary clinics, your veterinarian may prefer to have the samples tested at an outside laboratory that has specialized equipment and personnel with advanced training in microbiology. Your veterinarian will carefully take a sample from a site on your pet that is typical for the infectious disease. Samples are examined under a microscope, as well as cultured (grown on various substances) and then examined for the growth of colonies of the suspected organisms. Sometimes the bacteria have to be tested with different antibiotics to determine which one will be most effective. This takes a little longer but helps your veterinarian avoid treatment with an antibiotic that is not effective. Depending on the disease suspected, or if your pet is very sick, your veterinarian may start treatment with broad-spectrum antimicrobial drugs while waiting for specific test results.
Also see professional content regarding laboratory tests.