Opting for additional investigations : practical sampling procedures

Additional investigations, especially laboratory analyses, are key tools in current veterinary practice. However,they should be used resourcefully, since the number of analyses performed is often a key factor in how relevantly the results have been interpreted. It is important to factor in notions of sensitivity, specificity and positive or negative predictive values when developing a sampling scheme and during the results interpretation phase.Before leading additional investigations, it is first necessary to define the objective, since it is this objective that will govern the decision as to which method(s) will be used, and thus the sampling scheme. Practical sampling procedures are given for the main situations where we are likely to use additional investigations, i.e. screening, diagnosis, prevalence estimates, germ elimination, and searching to identify infection dynamics.