Medical diagnosis is the result of a series of empirical probability evaluations based on the physician’s professional experience, skills, clinical reasoning capability, intuition, and knowledge of the persons, family groups and population with whom he/she operates, as concerns the frequency of the various pathologies, their possible familiar aggregation, the people’s social conditions and life style, and the environmental factors involved.

Based on all this, on the outcome of the interview with the patient, on the collected anamnesis data, on the symptoms complained of by the patient, and on the clinical signs detected through physical examination, the physician may already be able to formulate, in a small number of cases, a certain or highly probable diagnosis.
In most cases, the physician will only be able to formulate one or more diagnostic hypotheses to be verified by means of a number of laboratory and instrumental diagnostic tests. This process is defined as differential diagnosis.

The key point of the process is that, although a diagnosis may be correct, it may not necessarily be appropriate (for example, if the diagnosis has been formulated by using redundant diagnostic tests, i.e. tests which are unnecessary, unjustifiably expensive, or uselessly risky for the patient).

The diagnostic tests available today in medical practice are numerous and continually evolving, and the physician’s choice of the tests to be made for a specific case can be very complex. It is apparent that the prescription of one or more tests can become particularly critical for general medicine physicians (GMP) who have to work transversally in different medical fields and who are often the patient’s first contact.

The main risks associated with test selection are essentially two: 1) overuse of diagnostic tests, resulting in unjustified higher costs for the National Sanitary System (NSS) and negative effects on the patient’s health, and 2) underuse of diagnostic tests, due to limited knowledge of an excessively broad offer, which may lead to unsuccessful diagnosis.

This situation has led several national and international medical/sanitary organizations, in recent years, to identify criteria to ensure performance quality (prescription of diagnostic tests and pharmacological treatments) and cost limitation, especially on the basis of outcome evaluations (evidence-based medicine) indicating the degree of effectiveness of a performance with beneficial effects on the patient. In this context, it is worth mentioning the study carried out by the Committee on the Quality of Health Care of the National Academy of Science in the United States (in Crossing the quality chasm: a new health system for the 21st century. Washington:National Academy Press; 2001), which identifies safety, effectiveness, timeliness, efficiency, equity and patient centrality as the targets of the National System of the 21st century.It is in this context that the concept of diagnostic appropriateness has recently grown and become increasingly widespread in the medical field.The appropriateness of a diagnostic test for a given pathology is not only determined by its accuracy, which can be expressed in terms of sensitivity and specificity, but also by several other factors: costs, access and outcome wait times, safety and tolerability for the patient, as described, for example, in: Ferrante di Ruffano L., Hyde C.J., McCaffery K.J. Bossuyt P.M.M. and Deeks J.J., “Assessing the value of diagnostic tests: a framework for designing and evaluating trials”, British Medical Journal. 2012; 344-352.

The appropriateness concept extends to the entire diagnostic path. In fact, the physician’s goal is to identify the disease that is most likely affecting the patient by starting from the collection of anamnesis data, symptoms and signs, and then by selecting the tests necessary for making the differential diagnosis, along a diagnostic path that is accurate, effective, fast, safe and economical, i.e. appropriate.

In this regard, it is apparent that the physician’s capabilities would be improved if he/she could choose from a number of appropriate diagnostic paths and could know a priori how much the prescription of one or more tests would effectively refine the differential diagnosis in terms of costs and benefits for the patient and for the NSS.
In general, the automatic and computerized systems used as a support for clinical diagnoses rely on a general knowledge base (epidemiological data, interactions between drugs, guidelines, etc.), to be integrated with the patient’s specific data (personal information, anamnesis, symptoms, signs). The data are then processed in order to formulate diagnostic hypotheses through the use of information theories and technologies (simulations, bioinformatics algorithms, statistical procedures, artificial intelligence systems).
Several attempts have been made in the past to develop software, or more generally ICT systems, which could help ph