[Predictive values of the usual biologic tests for the detection of human immunodeficiency virus infection....

This paper tries to review what is scientifically known about the predictive values of biological tests of HIV infection. The epidemiological situation for that infection is characterized by two facts: the very high values of sensitivity and specificity which are close to unity; the prevalence of seropositivity which is on average--at least in western countries--, very low (except for some small specific groups). Under those conditions, Negative Predictive Values are always very close to unity, and the percentage of false negative tests is extremely low. Things are quite different for Positive Predictive Value, which varies very rapidly with very small shifts or uncertainties about specificity and prevalence. In the case when prevalence is very low (general population screening) and at the same time specificity is not excellent (that means < 0.99 or even < 0.995), Positive Predictive Value is very poor and the proportion of false positive tests rather important. Indeed the analysis of scientific literature, using the method of "best synthesis evidence", reveals numerous discrepancies as to the value of specificity among different tests. Figures vary a lot from one study to another. It is not obvious which screening strategies are concerned by the results, which finally entail a strong statistical uncertainty. Finally, the figures published in the literature are given by high standard laboratories. One may fear the tests realized in routine laboratories are less reliable. As a conclusion, let us say that despite their very good quality, the biological tests, when used separately, should not be trusted without strong previous criticism when applied to samples of the general population. Any biological screening should be preceded by a clinical examination, including a precise inquiry, in order to detect people at risk, that means with a high prior probability. Clinical dialogue has moreover another great interest: it allows health consulting and education, and calls for personal responsibility for both seropositive and negative subjects. It is the best choice of method to reach a high preventive effectiveness.