Blood Biochemistry of Lower Vertebrates

Introduction Blood biochemistry profiles are often used to assess the physiologic status of lower vertebrate patients, such as fish, amphibians, reptiles, and birds. However, there is a general lack of controlled studies designed to clarify the meaning of changes in the blood chemistries of these animals compared to those of domestic mammals. Therefore, the clinical chemistry of lower vertebrates has not achieved the same degree of critical evaluation as demonstrated in domestic mammalian medicine. Currently, interpretations of blood biochemistries of these animals are considered the same as for domestic mammals with the consideration that external factors, such as environmental conditions, have a greater influence on the normal physiology and health of the ectothermic vertebrates [ectotherms] compared to endotherms. Species, age, gender, nutritional status, season, and physiological status influence blood biochemistries of the lower vertebrates, especially the ectothermic species [1-3]. This makes interpretation of blood biochemistry results challenging. Normal reference values for specific blood biochemical tests for a few species of lower vertebrates have been reported. Environmental conditions and physiological parameters such as nutritional status, gender and age often have not been taken into consideration when establishing reference intervals, making them less meaningful. Methods of sample collection, handling, and biochemical analysis are additional sources of variation in the published reference values. Therefore, published references are generally used as a broad guide to interpretation of blood biochemical results in lower vertebrates. Because of the difficulty in obtaining meaningful reference intervals for these exotic species seen in clinical practice, most clinicians utilize decision levels when assessing their lower vertebrate patients. Decision levels are threshold values above or below which a decision is made to respond to a value of an analyte. The response may vary from repeating the test or ordering additional tests to treatment of the patient. Decision levels may be obtained by utilizing published reference intervals and applying the values to those obtained in the laboratory used by the hospital. Decision levels may vary to some degree among clinicians, depending upon laboratory results and experience. Values suggested in this text are general guidelines that can be used as decision levels when evaluating each analyte in the avian and reptilian blood biochemical profile. The process of evaluating the blood chemistries of a avian or reptilian patient can be refined by obtaining a set of normal values from that patient housed under a given set of environmental and nutritional parameters. Therefore, when that patient becomes ill, a more meaningful set of reference values specific for that patient can be used to evaluate the chemistry results.