Samples may be obtained from the avian patient in a number of ways. The least stressful and easiest method involves clipping one or more toenails and allowing the blood to flow freely into tiny capillary tubes that contain an anti-coagulant Blood smears are made from a single drop of blood placed on a microscope slide or cover slip. Blood can also be withdrawn from the jugular or a peripheral vein using a syringe equipped with a very small needle. This latter method is often less stressful than nail clipping when dealing with the smaller caged birds (budgies, canaries, finches, etc) and may be necessary if a relatively large blood sample is required. Only very small volumes of blood are required by the laboratory. Therefore, there is no caged bird that cannot be examined in this manner. Chemical cautery agents are used to stop the nail from bleeding, and finger pressure is used to prevent excessive bleeding when blood is withdrawn from a vein using a needle and syringe. The blood sample can be examined in 2 different ways. Analysis of the cellular portion of the blood yields red and white blood cell counts. These are useful in diagnosing anemia and determining whether a patient is experiencing enough of an insult to its system to cause changes in the circulating white blood cells. These changes either influence the total number of white blood cells circulating in the peripheral blood or the proportions of the 5 different types of avian white blood cells, or both. Blood smears can be stained and examined for the presence of blood parasites and to obtain information about all the blood's cellular components.
The fluid portion of the blood (plasma) is also examined (blood chemistry evaluation) and yields information about the biochemical status of the patient and the integrity of the patient's vital organs (liver, kidneys, etc). This information provides the clinician with specific diagnoses, such as diabetes and gout. In other cases, biochemical profiling of the blood indicates the organ systems involved and the severity of the disease. Blood workups provide information that enables the avian veterinarian to understand the severity of the patient's condition, to know the extent of the disease, and to follow the patient's clinical course with successive blood samples. Serial laboratory testing enables the clinician to follow the patient's progress and make changes in treatment much more rapidly than would otherwise be possible by simply monitoring the patient's visible response (or lack of response) to treatment.