[Theoretical objective evaluation of the value of a diagnostic criterion. Application to antinuclear antibodies for the diagnosis of systemic lupus erythematosus].

The value of various types of anti-nuclear antibodies (ANA) for the diagnosis of systemic lupus erythematosus (SLE) was calculated in a population of adult patients with chronic polyarthritis. The aim of this study was to demonstrate the value of calculating the predictive value of a test applied to a particular clinical situation. It was conducted on the basis of epidemiological and laboratory data from the literature. The calculations show that the presence of ANA in immunofluorescence only slightly increases the probability of the diagnosis of SLE (7%). On the other hand, these antibodies are an example of a very sensitive test which, when it is negative allows the diagnosis to be almost totally excluded, while anti-Sm antibodies are very specific and their presence allows the diagnosis to be confirmed. Anti-nDNA antibodies have intermediate features, but their diagnostic performance increases with the level of radioactive n-DNA binding chosen as the level of positivity; in this example, for a level of binding of more than 50%, the predictive value of anti-nDNA antibodies is equivalent to that of anti-Sm antibodies.