There are several categories of diagnostic tests that may be performed to help your veterinarian determine the cause of your pet’s illness.
Clinical chemistry is the study of the chemical composition of a sample. Usually, the sample is the liquid portion of blood (serum or plasma), although other body fluids may also be studied. Clinical chemistry tests are important for determining how well different organs (kidneys, liver, etc.) are working. They can help identify specific disorders, such as diabetes or pancreatitis. These tests may also be used to monitor how your pet is responding to treatment.
The study of individual cells, their structure and origin, function(s), and death is known as cytology. Specialists in this field (pathologists) can provide a veterinarian with information about the cells in your pet’s body. Samples of tissue (taken using a fine-needle biopsy) or fluid are collected, then slides are prepared and stained for microscopic examination to determine the kinds of cells present. Pathologists are often called upon to identify cancerous cells or determine whether a tumor is benign or cancerous (malignant). The presence of infectious agents can also be determined. Some microorganisms can be identified (some yeast forms have a unique appearance), but bacteria require microbiology testing for identification.
Fluid analysis is the study of bodily fluids other than blood (urine, joint fluid, etc). Specialists in analyzing body fluids work closely with other specialists to help provide information about the health of an animal. Typically, fluid analysis includes checking the sample for cells and proteins. Clinical chemistry testing for certain compounds may also be performed.
Hematology is the study of cellular elements of blood (red blood cells, white blood cells, and platelets), and how these elements change in health and disease. The most common blood test is a complete blood count (CBC). This test determines the number and types of cells circulating in the bloodstream and provides basic information about anemia, inflammation, and clotting. Determining the number of red blood cells, their size and shape, and their hemoglobin content (the molecule that carries oxygen) helps identify disorders such as anemia. Counting the different types of white blood cells gives information about inflammation, which could be due to an infection or other cause. Platelets are also examined during a CBC; changes in platelet numbers or appearance can help identify blood clotting disorders.
Histology is the study of the microscopic structure (anatomy) of animal and plant tissues. Experts in histology (called pathologists) examine small tissue samples to determine whether they are normal or diseased. Pathologists have studied the causes and effects of diseases and can often point to a reason for abnormal tissue arrangements or cells.
Small tissue samples will often be sent to a pathologist if your veterinarian suspects conditions such as cancer or other diseases that cause tissue changes.
Microbiology is the study of small organisms such as bacteria, viruses, fungi, and other single-celled life forms. In a veterinary laboratory, specialists in microbiology can perform many tests looking for signs of infection. A common procedure includes first growing (culturing) and then identifying bacteria, viruses, and fungi. Bacteria can be tested to see which antibiotics should be effective in eliminating them from the body. Some microorganisms are difficult to grow in the laboratory, and antibodies or other chemicals may be used to detect the presence of microorganisms in a sample. Samples from your pet, that can be used to culture microorganisms include blood, urine, feces, secretions from the nose or lungs, and swabs taken from a wound or abscess.
Serology is the study of blood serum and other body fluids. Most serologic tests determine the level of antibodies (called the titer) that are present and reactive against a particular infectious microorganism. A high level of antibodies, or an increase in their level from one sample to another taken a few weeks later, shows that an animal has been exposed to the microorganism and its immune system has produced antibodies against the infectious agent. Commercial test kits are available for a wide range of serologic tests. The test kits are used on a regular basis by both in-house and outside laboratories to test for diseases such as heartworm disease, feline leukemia virus infection, Lyme disease, equine infectious anemia, and many others.
Toxicology is the branch of science that studies poisons and how they affect animals. If your veterinarian suspects that your pet has been poisoned, samples will be collected for toxicologic tests to identify the poison and the amount of damage it may have caused. Some common poisons can be quickly identified. Rapid identification of a poison can be critical for your pet’s survival. In other cases, samples may be sent to an outside laboratory that can accurately test for a much wider range of poisons. If your pet has eaten something toxic, your veterinarian may ask you to bring a sample of it with you for testing.
Also see professional content regarding veterinary medical tests.