52 REPTILIAN BIOCHEMICAL ANALYSIS
1 What are some important principles to understand about the use of biochemical analysis in reptiles?
a. Current understanding of reptilian biochemical changes in disease is less than the knowledge of biochemical changes in birds and mammals, primarily because of the lack of scientific studies on reptilian biochemistry.
b. Biochemical reference intervals can vary greatly within and between species of reptiles (even more so than in birds). This variation may be caused by several factors, including differences in nutrition, environment/geography, instrumentation, methodology, number of animals examined, age, and quality of samples.
d. Because of interspecies variations in analytes, published reference intervals (or those provided by the laboratory) should be used as a guide and not as an absolute when interpreting biochemical data.
e. Plasma (lithium heparin plasma only) should be used for reptile biochemical analysis. Heparinized plasma maximizes the available sample volume for analysis and minimizes artifacts related to prolonged contact with the cellular components of blood. Plasma should be promptly separated and analyzed.
2 How can in vivo or in vitro hemolysis affect clinical chemistry parameters?
a. Direct interference with the measurement of analytes (e.g., hemoglobin interference with optical measurements). The magnitude of interference with the measurement depends on the methodology and instrumentation used.
b. Release of erythrocyte contents that contribute to similar plasma/serum constituents (e.g., AST, LD). There is no direct interference with the actual measurement method. This effect is pronounced when erythrocytes contain higher concentrations of the constituent than the concentration present in plasma/serum.
3 What are causes of hyperglycemia in reptiles?
a. Glucocorticoids: endogenous (“stress”) or exogenous; may be associated with concurrent diseases such as infections
5 What biochemical tests are of use when evaluating the urinary system?
Uric acid, calcium, and phosphorus concentrations are used to evaluate the urinary system.
6 How are uric acid concentrations used in diagnosing kidney disease?
b. Uric acid is not a sensitive indicator of renal disease because it is primarily secreted in the proximal tubules, and the glomerular filtration rate (GFR) must be decreased significantly to detect increases in uric acid concentrations. Some reptiles with renal failure may have normal concentrations of uric acid because functional impairment may not be of sufficient magnitude to produce increased uric acid concentration.
c. In carnivorous reptiles, uric acid concentrations may increase significantly after feeding and peak a day after a meal. This increase reportedly should not exceed 15 mg/dl in healthy individuals.
d. Despite the drawbacks, uric acid is regarded as a useful marker of renal disease if reference intervals for the species in question are available.
7 How are calcium and phosphorus concentrations used in diagnosing kidney disease?
a. In renal disease, urinary excretion of phosphorus may decrease and result in increased plasma concentration.
c. Renal disease is also suggested when the product of calcium and phosphorus concentration is greater than 55 mg/dl. However, this is not a reliable indicator of renal disease in adult female iguanas.
