HIV-1: absence of infection in subjects with indeterminate western blot.

The search for specific antibodies against the Human Immunodeficiency Virus type-1 (Ab anti HIV 1), using an immunoenzymatic test and a subsequent confirmation test (Western Blot-WB) in patients who were previously positive or borderline at the first test, singled out from about 12500 tested subjects, fifteen patients with indeterminate WB (WBi) for the presence of an abnormal band. The presence of p24 was predominant in those WBi (about 50%); generally p24 was the only band found. In all serum samples with WBi, the viral antigen p24 (Ag p24) was absent. In 3 subjects with WBi, after at least six months from the first test, not only did the same pattern persist but also the search for VIH-1 DNA sequence using the polymerase chain reaction (PCR) gave a negative result. According to our experience and the literature on the subject, we suggest that patients with low risk of infection and whose WBi does not modify with time have a remote possibility of being infected by HIV.