The diagnostic utility of the febrile agglutinin tests

The purpose of our study was to analyze the use of febrile agglutinin (FA) serologic tests in the diagnosis of Salmonella (typhi and paratyphi), Rickettsia, Brucella, and Francisella infections. Data were collected in a retrospective chart study of 202 titer requests covering a 42-month period at our teaching hospital. We found that no diagnoses were made by utilizing complete six-antigen FA panels. Three cases of infection were diagnosed serologically, all three with more discriminately selected single-antigen titers. These three cases each had a positive epidemiological history suggestive of disease prior to ordering FA tests. Our data suggest that the FA tests (especially the Salmonella group antigen) are an overutilized set of laboratory tests and are often difficult to interpret. It is much more important to make a diagnosis based on clinical findings and epidemiological criteria.