Different diagnostic strategies for different settings

Abstract

Diagnostic strategies should always take into consideration the setting in which they are administered. The predictive value, positive or negative of a clinical sign or diagnostic test has a different weight in family medicine than in the hospital setting. Many tests have not been formally evaluated in primary care; unfortunately, very often low prevalence settings are used to conduct screening in these populations, and often result in unrealistically high prevalence estimates for chronic disease and these results are then used to conclude that General Practitioners are not good at detecting diseases. In primary care, the prevalence and incidence of disease differs from what appears in the hospital setting, and severe disease occurs less frequently in general practice than in hospital because there is no preventive selection. This requires a specific probability-based decision-making process, based by the knowledge of patients and the community. In primary care, the diagnostic strategy should begin with complaints and symptoms and address uncertainty and complexity, using step-by-step strategies, including watchful waiting, presumptive symptomatic treatment, and focusing on low-tech strategies. The diagnostic process There are 2 fundamental strategies in the diagnostic process in Medicine. (Unpublished data: Terry Shaneyfelt, https: //ebmteacher.com/open-teaching-resources/ accessed 28/11/2020): i) pattern recognition: e.g. shingles, where the presence of specific signs and symptoms is pathognomonic of the disease; ii) probabilistic: e.g. deep vein thrombosis, where the probability of a disease is influenced by the diagnostic test accuracy.1 The pre-test probability is the probability that a patient is affected by a disease, prior to any further diagnostic studies. In the probabilistic diagnostic paradigm, we start form the pre-test probability and after the test result we have a revised probability (post-test probability). Table 1 shows how can we estimate the pre-test probability. When to use a supplementary diagnostic test? Figure 1 shows the diagnostic process that should guide us in establishing a diagnosis. If further testing is needed, then the next step is to choose a diagnostic test. Because there are often multiple tests that could be ordered for a given disease we need to pick the right one for the situation. How to choose a diagnostic test? Before ordering a test, doctors need to think carefully of the pre-test probability. What do we want to do with a test? Rule in a disease or rule out a disease? In order to do this, doctors need to compare the operating characteristics of a test before selecting one, and above all, to think about what they will do with the results of a test. Comparing the operating characteristics of a test before selecting one Table 2 illustrates the role of testing. Do we need a sensitive or a specific test? It depends on the role of testing (rule in or rule out). When we want to rule in a disease, we need a specific test, while when they want Geriatric Care 2021; volume 7:9538 Correspondence: Ferdinando Petrazzuoli, Center for Primary Health Care Research, Department of Clinical Sciences, Lund University, Box 50332, 202 13, Malmö, Sweden. Tel.: +4640391363 Fax: +4640391370. E-mail: ferdinando.petrazzuoli@med.lu.se