and the diagnostic test utilized has high specificity. Negative predictive value can be calculated by dividing the number of true negative test results by the total number of negative test results (true negatives + false negatives). A test will have a high negative predictive value when the disease is not common in the population and the diagnostic test utilized has high sensitivity. See Figure 4.2.
Figure 4.2 Sensitivity, specificity and predictive value. TP, true positives; TN, true negatives; FP, false positives; TN, true negatives.
Understanding these measures of accuracy is critical to designing rational diagnostic testing strategies for both individual animals and the shelter population as a whole. With each diagnostic test employed, there comes a risk of either false positive or false negative test results that may have a far‐reaching impact. Therefore, such decisions should only be made after an assessment of the cost–benefit ratio for the individual animal or shelter population and the acceptance of the risk posed by erroneous results. The following questions should be considered:
Could an inaccurate test result lead to euthanasia?
How would an inaccurate test result impact other animals in the shelter or community?
Could treatment for a disease not present or lack of treatment for a disease that is present negatively affect the animal's well‐being in the shelter or its disposition? How might that treatment impact other animals in the shelter or community?
How could an inaccurate test result burden an adopter? Might it discourage adoption altogether?
What are the costs of both accurate and inaccurate test results (e.g. money, time)?
Once it has been decided to perform diagnostic testing and the consequences of both positive and negative test results have been considered, a strategy can be developed. When there is a substantial risk for negative consequences from a false negative result, then a strategy that results in a high negative predictive value should be developed. An example of this can be seen with canine parvovirus testing in a dog with vomiting and diarrhea. Obtaining a false negative test result would allow the disease to progress and allow for continued transmission to other dogs in the shelter or community. If a negative antigen test result is obtained, repeating the original diagnostic test or using additional diagnostics such as a complete blood count or blood smear evaluation to acquire evidence in support of the original negative test result will increase the sensitivity of the testing strategy, minimize the risk of a false negative, and increase the negative predictive value of the result. When there is a substantial risk for negative consequences from a false positive result, then a strategy that results in a high positive predictive value should be developed. An example of this can be seen with canine parvovirus testing in a shelter for which treatment is not possible and infected puppies are euthanized. In this case, the consequences of a false positive result are extreme, so limiting testing to dogs with clinical signs of GI disease will limit testing to a population in which the disease is more common, minimizing the risk of false positives and increasing the positive predictive value of test results.
4.6 Standard Operating Procedures
4.6.1 Protocol Development and Staff Training
The definitive diagnosis of a disease is legally defined as the practice of veterinary medicine in many jurisdictions and should be performed only by veterinarians or under direct veterinary supervision. However, the establishment of SOPs, including diagnostic testing protocols, is not only a best practice for animal shelters but is also an essential component of meeting industry guidelines for shelter animal care. Such protocols must be written, detailed, current, accessible to staff and volunteers and should be developed with veterinary input. Protocols should define common illnesses, offer initial management steps, and detail the expected course of disease and response to treatment (Newbury et al. 2010). Protocols that pertain to disease diagnosis should describe the indications for diagnostic testing, the performance of common diagnostic tests, recognition and response to adverse treatment effects, and discuss the documentation of testing procedures (Association of Shelter Veterinarians 2014). Though diagnostic testing protocols should be veterinary‐directed, it is important that staff and volunteers are included in their development to ensure understanding and assess feasibility (Steneroden 2004).
Once protocols are established and written, staff must be trained on their implementation. Training techniques should be targeted toward the desired outcome which, in the case of diagnostic testing, is typically the performance of new skills. Therefore, performance and competency‐based strategies should be utilized and generally include: a verbal and written description of the skill to be acquired, demonstration of the target skill, practice of the target skill, performance feedback, and repetition until mastery. Mastery of the skill in a simulated learning environment should be followed by training in an actual work scenario (Parsons et al. 2012). Training should be continuous to ensure the maintenance of skills, account for the turnover of shelter staff and volunteers as well as changes in standard procedures and should involve periodic observation of staff to ensure adherence to established protocols (Steneroden 2004).
4.6.2 Diagnostic Algorithms
The use of medical diagnostic algorithms is popular in both human and animal healthcare. Such an approach is thought to minimize unnecessary testing, control costs, and provide uniform quality care (Mushlin and Greene 2010). It is important to remember that such tools should be used with caution, particularly in complex cases, and should not be used as the sole means of disease diagnosis. However, in routine clinical scenarios, they have demonstrated enhancements in diagnostic accuracy when used in combination with clinical assessment (Riches et al. 2016). The following diagnostic algorithms are provided to help the shelter medicine practitioner obtain a diagnosis in common clinical scenarios in which infectious diseases are likely to be involved. See Figures 4.3–4.5.
4.7 Conclusion
A thoughtfully employed diagnostic testing strategy can ensure cost‐effective protection of animal health and welfare in the shelter environment. Practitioners need not dismiss diagnostic testing as unattainable or unrealistic simply due to resource limitations. In fact, many of the most clinically useful diagnostic tools require minimal financial investment and thoughtful use of timely, targeted testing can often be a more cost‐efficient strategy when all operational costs are considered. Careful use of the core diagnostic modalities—case history, physical examination, and response to treatment—will establish a sound treatment plan in many, if not the majority of shelter patients. With a modest budget, basic diagnostic supplies and equipment can be obtained allowing for a great spectrum of diagnostic capabilities through both primary and secondary diagnostic tests at a minimal cost. Such information can adequately guide the short‐ and long‐term care of a variety of medical conditions in the shelter environment. Resources should also be reserved for advanced diagnostic laboratory testing and disease outbreak response when indicated.
Shelter practitioners should have a keen understanding of the benefits and drawbacks of each testing modality in order to select the most appropriate test for a given clinical situation and accurately interpret the results. Diagnostic testing protocols should be developed for both individual‐ and population‐level health maintenance; they should be written and accessible. Such protocols should be designed by a veterinarian with knowledge of the animal population as well as familiarity with shelter
