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A routine hemogram can assist in the diagnosis of some infectious and inflammatory diseases, lymphosarcoma and trauma with blood loss. Results of routine blood chemistry tests, many of which can be obtained at animal side by the use of convenient point‐of‐care devices, assist in defining many metabolic diseases affecting the nervous system, particularly liver failure, hyperammonemia, renal failure/uremia, hypocalcemia, hypercalcemia, hypomagnesemia, hypokalemia, hyperkalemia, and hypoglycemia. Special serum enzyme and other assays and organ biopsies may be performed to confirm liver and muscle disease, and routine urinalysis has its place in monitoring pigment excretion in systemic diseases (Figure 3.1). Detecting circulating pyrrolic metabolites of pyrrolizidine alkaloids from plants responsible for huge losses of herbivores from liver disease is possible,¹ and in future more use may well be made of detection of plant toxins in blood samples of patients suspected of suffering other plant poisonings. Assays for toxic chemicals and their effector compounds in body fluids and tissues depend on knowledge of the particular intoxicant, e.g., cholinesterase activity for organophosphate intoxication^2,3 and cantharidin for blister beetle poisoning.⁴

Only rarely do pituitary tumors result in overt neurologic syndromes such as blindness and collapsing episodes, but those that are functionally excreting tumors can often be detected using current endocrinologic testing procedures.^5,6

Specific serum antibody titers, particularly when assayed on acute and convalescent sera, are helpful in diagnosing infectious diseases such as equine viral encephalitis, equine infectious anemia, equine herpesvirus‐1 myeloencephalopathy, louping ill, malignant catarrhal fever, pseudorabies, and bovine leukemia virus infection. Blood and tissue toxin and nutrient concentrations can assist in diagnosing intoxications and nutritional disorders.