When your pet is sick, the veterinarian might order blood tests, imaging, or other laboratory tests to find out what’s wrong and how serious it is. Some tests are done right at the clinic, while others are sent to specialized laboratories. The test results help the vet figure out the cause of illness and plan your pet's treatment.
Hematology
Hematology is the study of the cells in blood: red blood cells, white blood cells, and platelets. The most common blood test is the complete blood count (CBC). A CBC shows how many and what types of blood cells are in your pet's blood.
Examining red blood cells—how many there are, their size and shape, and their hemoglobin (the molecule that carries oxygen)—helps identify anemia (low red blood cell count) and other disorders.
Counts of white blood cells (and counts of white blood cell types) can show inflammation or infection.
Changes in platelet number or appearance can point to clotting problems.
Clinical Chemistry
Clinical chemistry is the study of the chemicals that make up a sample, usually the liquid part of blood (serum or plasma). Measuring different markers, electrolytes (like sodium or potassium), blood sugar, and other chemicals helps tell how well organs like the liver and kidneys are working and can diagnose conditions like diabetes. Chemistry profiles are also used to track drug levels or how well a treatment is working.
Cytology
Cytology is the study of individual cells. Vets collect a sample (fluid or cells). Cell types can be identified on microscope slides. Clinical pathologists are experts in this field who can help make a diagnosis, like whether a tumor is benign (not cancer) or malignant (cancer). Some infectious microbes (like bacteria and viruses) can be recognized on cytology, but others need special tests for identification.
Fluid Analysis
Fluid analysis is the study of body fluids other than blood, like urine or joint fluid. This kind of testing combines cytology (cell types) and chemistry (proteins and other chemicals). Specialists use fluid analysis to help provide information about an animal's health.
Histology
Histology is the study of the microscopic structure of tissues in the body. Vets send small tissue samples (such as a biopsy) to a lab. Specialists then examine the tissue to see whether tissue is normal or diseased and can often identify why the tissue has changed. Tissue samples are commonly sent when cancer or other diseases are suspected.
Microbiology
Microbiology is the study of bacteria, viruses, fungi, and other tiny organisms, or microbes. Lab specialists can culture (grow) and identify microbes from samples, like blood, urine, or feces, or from samples from an animal's nose, lungs, wounds, or abscesses (pockets of pus). Bacteria can be tested to find which antibiotics will work, although if a pet is very sick, vets sometimes start treatment before lab results come back. Some organisms are hard to grow, so other methods (like antibody tests) may be used.
Serology
Serology tests look for antibodies in blood or other fluids. An antibody level, or titer, shows whether a pet's immune system has seen a certain infectious agent before. A high titer or a rising titer between two samples taken weeks apart shows exposure or infection. Vets can test for diseases such as heartworm, feline leukemia, Lyme disease, and equine infectious anemia.
Toxicology
Toxicology is the study of poisons, or toxins, and how they affect animals. If your vet suspects poisoning, they might collect samples to identify the toxin and assess damage. Some poisons are identified quickly, which can be critical for treatment. Other samples may be sent to specialized labs that test for more types of toxins. If your pet ate something toxic, the vet might ask you to bring a sample of it.
