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Tests Routinely Performed in Veterinary Medicine

By Morag G. Kerr, BVMS, BSc, PhD, Cbiol, FIBiol, MRCVS ; Jimmy C. Lattimer, DVM, MS, DACVR, DACVRO, Veterinary Medicine and Surgery, Veterinary Medical Teaching Hospital, University of Missouri

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 office or clinic, samples may be sent out to a laboratory, or you may be asked to take your pet to a special test facility.

The Veterinarian

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 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, routine examination of 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 abnormal heart, lung, or digestive system sounds that may indicate 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 is going into, or is already in, shock. Long 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.

Specialized Tests

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 assess 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.

The In-house Laboratory

Most veterinary clinics have at least basic laboratory facilities within their clinic. Several laboratory tests can be carried out in these facilities after the veterinarian collects the appropriate samples or after the pet owner collects the samples and brings 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.

Stool Samples

Stool samples may be collected by the pet owner prior to a visit to the veterinary clinic or they may be collected by the veterinarian. A small amount of the stool sample is prepared and then examined under a microscope. In some cases, a small amount of the stool is placed in a liquid and then examined with a microscope. These steps are used to detect the presence of the cysts of various parasites such as Giardia and Cryptosporidium. The eggs of other parasites, such as roundworms, hookworms, and tapeworms, can be found in stool samples. Larval or adult worms or tapeworm segments may also be observed.

Urine Samples

Analysis of urine samples (urinalysis) is important for detecting various types of urinary tract diseases. Because significant changes occur in urine if it is left at room or higher temperature for any length of time, the sample should be analyzed immediately after collection, or refrigerated and transported to the laboratory as soon as possible after collection. Urine samples should not, however, be frozen because freezing will change several important characteristics of the urine. The tests usually carried out on urine samples include examining the appearance, chemistry, and sediment.

Normal urine is typically yellow or amber in color and is usually 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 may include determining its specific gravity (density) and pH level and measuring the amount of protein, glucose, or fragmented blood cells, all of which can 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, while large numbers of white blood cells usually indicate an infection. Other solid components of urine, known as casts, are long tubular structures formed by the congealing of protein in the kidneys. Large numbers of casts may indicate kidney disease. Crystals may be present but are generally 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.

Blood Samples

Analysis of the numbers and structure of blood cells 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 3 common tests carried out using red blood cells: packed cell volume, hemoglobin concentration, and red blood cell count. All 3 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 5 main types of white blood cells . Neutrophils are the most common type of white blood cell. They engulf (“eat”) infectious particles such as bacteria. They increase in number during inflammation, infection, and short-term stress. A related type of white blood cell is the eosinophil. The number of eosinophils goes up during allergic reactions and some tissue injuries. Their number also goes up in response to certain tumors and parasites. Basophils are the least common type of white blood cell. They are also related to neutrophils and eosinophils. An increase in the number of basophils is associated with inflammation. Monocytes are large cells that serve mainly as phagocytes and increase in number during chronic diseases. 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.

The Outside Laboratory or Test Center

Many of the tests the veterinarian uses to diagnose disease require highly specialized instruments or equipment. In other cases, specific training is required for the technicians performing the tests. For these reasons, many veterinarians will either send the samples to an outside laboratory or refer the patient to a special test facility. Some of the tests conducted are similar to those available in the clinic, but the availability of advanced testing equipment in a specialized facility may offer advantages in speed and accuracy. For example, the specialized laboratory may be able to more easily spot and identify abnormally shaped 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 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 signs and a history that could make it difficult to determine the problem. The basic group of blood tests for pets includes total protein, albumin, globulin (calculated as the difference between total protein and albumin), urea, creatinine, alanine amino transferase (ALT), and alkaline phosphatase (ALP). 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

Test

What the Results may Mean

Total Protein

Increases due to dehydration or inflammation; may decrease due to bleeding, malnutrition, or congestive heart failure

Albumin

Increases due to dehydration; may decrease due to bleeding, congestive heart failure, or liver failure

Globulin

Calculated as the difference between total protein and albumin

Urea

Increases due to certain dietary excesses or deficiencies, congestive heart failure, kidney failure, or a ruptured bladder; decreases may be due to liver failure or low levels of dietary protein

Creatinine

Increases may be due to kidney disorders, muscle damage, or a ruptured bladder

Glucose

Increases may be caused by diabetes or short-term stress; decreases may be found in cases of neurologic disease or malnutrition

ALT and ALP

Increases in these enzymes may indicate liver damage, muscle damage, or increased thyroid gland activity

It is important to identify the specific bacteria or other organisms causing an infection so that your veterinarian can carry out 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 very carefully take a sample from a site on your pet that is typical of the disease or infection process. 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.

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