A number of immunological and serologic diagnostic tests have been investigated because of the difficulty with interpreting the isolation of Candida from the urinary and respiratory tracts as well as confirming the diagnosis of invasive candidiasis, especially in immunocompromised hosts. Some of these tests look promising; however, most are not commercially available for routine use. Several rapid antigen detection assays are available, including latex particle agglutination (LPA), enzyme immunoas-say, and radioimunoassay. Most assays detect mannan as the main Candida antigen. Some of these tests have a high rate of false negatives. The LPA is the easiest to perform and has been shown to be useful in quantitation of Candida. Using a titer of 1:4 or above as a positive result, it has an excellent specificity of more than 90% but at best a sensitivity of only 70%. The LPA is more useful for monitoring response to therapy than diagnosis because there is some correlation with decreasing titers and successful antifungal treatment. The enzyme immunoassay is a rapid and quantitative test for Candida antigen that has excellent specificity but has poor sensitivity and cannot provide species information and therefore is not very useful.
Antibody tests are not routinely recommended because there is a high rate of false negatives, especially in the immunocompromised patients. Complement fixation and indirect immunofluorescent antibody tests are not very helpful in the diagnosis of disseminated disease. Deoxyribonucleic acid probes are used as a rapid diagnostic test for vulvovaginal candidiasis with excellent specificity (99%) and good sensitivity (75%). Candida skin tests are not useful and should not be used because they cannot distinguish between colonization and invasive disease. Assays to measure levels of D-arabinitol, a metabolite of pathogenic Candida species in the urine and serum, have been developed but are expensive and difficult to perform. The measurement of the d/ L-arabinitol ratio appears to be of diagnostic value in invasive disease. This test looks promising but is still under investigation.
Candida species can be rapidly detected in urine, blood, and sputum by polymerase chain reaction (PCR); however, detection may not mean invasive disease in a colonized patient. Detection of Candida by PCR using clinical isolates followed by restriction fragment length patterns looks promising for rapid diagnosis of disseminated candidiasis. These tests are not routinely available and are under further investigation. In an outbreak, analysis of the isolates can be accomplished by two genotyping methods: electric field gel electrophoresis and PCR-based direct sequencing.
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