Tests Routinely Performed in Veterinary Medicine

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.

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.

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.

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.