Practical Approaches for Studying Sea Turtle Health and Disease
393
pathologic conditions, either with environmental factors such as habitat
type, diet, water temperature, and season or with specific known events such
as oil spills and algal blooms, will indicate areas for further research to
investigate possible pathophysiologic mechanisms.
15.3.1.2 Test Selection
Decisions regarding what tests and procedures to include in a health assessment
program are critical because, as stated, these parameters define the depth of the
assessment. Health assessment will be as good as the diagnostic tools that are used,
the reference ranges that are available for the species being studied, and the skills
of the investigator at recognizing turtles with abnormal signs and interpreting test
results. The range of diagnostic tools that can be used will be narrower in the field
situation than in a laboratory of a veterinary clinic.
Minimally, any health assessment program should include baseline morphometric
data and a physical examination (discussed in Section 15.4.4). Screening tests should
be included if possible. When the purpose of the study is to establish reference ranges
for specific parameters, these basic observations and data are needed in evaluating
individuals for inclusion in or exclusion from the reference population, and the definition
of the reference population will include the criteria used to select them as “normal”
(Walton, 2001b). It is difficult to give specific recommendations beyond this because
test selection will be based on the specific health questions and hypotheses of interest.
There are, however, general considerations in selecting tests and parameters,
study design, and interpretation. One should have a basic physiological understanding of the value and limitations of a specific test — i.e., what the results can indicate
about the animal and, equally important, what they cannot. No single test will give
a complete answer regarding the health status of an animal. Although each test may
provide specific objective information, at best, results will indicate a range of possible explanations. One should be aware of other tests that may be needed to confirm
a test result or to support a particular interpretation, and consider incorporating these
in a tiered approach. In a disease investigation, the significance of individual test
results will be integrated with the results of other supporting data and interpreted
in light of the animal’s clinical condition. Interpreting health parameters in a population of apparently healthy individuals is more problematic.
15.3.1.3 Interpretation of Out-of-Range Data and Positive
Test Results
For tests that yield quantitative data, such as cell counts, enzyme activities, and
analyte concentrations, results are interpreted relative to a reference range for that
population. A critical factor in interpretation is that reference ranges should be
representative of the population being assessed (Walton, 2001b). There is a high
probability of misinterpreting a result as abnormal if the reference range is inappropriate. For example, available reference ranges for blood biochemistry parameters for all turtle species are quite limited, so interpretation of blood values from
an individual turtle is often based on extrapolation from other species and limited
1123 book.book Page 393 Monday, November 11, 2002 11:11 AM
393
pathologic conditions, either with environmental factors such as habitat
type, diet, water temperature, and season or with specific known events such
as oil spills and algal blooms, will indicate areas for further research to
investigate possible pathophysiologic mechanisms.
15.3.1.2 Test Selection
Decisions regarding what tests and procedures to include in a health assessment
program are critical because, as stated, these parameters define the depth of the
assessment. Health assessment will be as good as the diagnostic tools that are used,
the reference ranges that are available for the species being studied, and the skills
of the investigator at recognizing turtles with abnormal signs and interpreting test
results. The range of diagnostic tools that can be used will be narrower in the field
situation than in a laboratory of a veterinary clinic.
Minimally, any health assessment program should include baseline morphometric
data and a physical examination (discussed in Section 15.4.4). Screening tests should
be included if possible. When the purpose of the study is to establish reference ranges
for specific parameters, these basic observations and data are needed in evaluating
individuals for inclusion in or exclusion from the reference population, and the definition
of the reference population will include the criteria used to select them as “normal”
(Walton, 2001b). It is difficult to give specific recommendations beyond this because
test selection will be based on the specific health questions and hypotheses of interest.
There are, however, general considerations in selecting tests and parameters,
study design, and interpretation. One should have a basic physiological understanding of the value and limitations of a specific test — i.e., what the results can indicate
about the animal and, equally important, what they cannot. No single test will give
a complete answer regarding the health status of an animal. Although each test may
provide specific objective information, at best, results will indicate a range of possible explanations. One should be aware of other tests that may be needed to confirm
a test result or to support a particular interpretation, and consider incorporating these
in a tiered approach. In a disease investigation, the significance of individual test
results will be integrated with the results of other supporting data and interpreted
in light of the animal’s clinical condition. Interpreting health parameters in a population of apparently healthy individuals is more problematic.
15.3.1.3 Interpretation of Out-of-Range Data and Positive
Test Results
For tests that yield quantitative data, such as cell counts, enzyme activities, and
analyte concentrations, results are interpreted relative to a reference range for that
population. A critical factor in interpretation is that reference ranges should be
representative of the population being assessed (Walton, 2001b). There is a high
probability of misinterpreting a result as abnormal if the reference range is inappropriate. For example, available reference ranges for blood biochemistry parameters for all turtle species are quite limited, so interpretation of blood values from
an individual turtle is often based on extrapolation from other species and limited
1123 book.book Page 393 Monday, November 11, 2002 11:11 AM