Description:
<jats:p>The diagnostic performance and usefulness of the Platelia antigen and antibody test (Bio-Rad) was investigated in a prospective study of haematological patients at risk for invasive <jats:italic>Candida</jats:italic> infections. Among 100 patients, 86 were eligible, of whom invasive candidiasis (IC) occurred in 12 (14 %), according to the criteria of the European Organization for Research and Treatment of Cancer/Mycoses Study Group. These included candidaemia due to <jats:italic>Candida albicans</jats:italic> (one patient) or <jats:italic>Candida tropicalis</jats:italic> (four patients), and hepatosplenic candidiasis (seven patients). The comparator group of 74 patients included 50 with febrile neutropenia alone and 24 with mould infections. A strategy was developed to determine diagnostic cut-offs from receiver operating characteristic curves with maximal sensitivity and, given this sensitivity, maximal specificity, both being greater than 0. In this patient population, these values were 0.25 ng ml<jats:sup>−1</jats:sup> for mannan (M) and 2.6 arbitrary units ml<jats:sup>−1</jats:sup> for anti-mannan (AM), which are lower than those recommended by the manufacturer. All patients developed at least one positive diagnostic M or AM result during the 10 days of persistent febrile neutropenia (PFN). The optimal overall performance was found when two consecutive positive tests for both M and AM were used [sensitivity, specificity, positive predictive value and negative predictive value (NPV) (95 % confidence intervals) of 0.73 (0.39–0.94), 0.80 (0.69–0.89), 0.36 (0.17–0.59) and 0.95 (0.86–0.99), respectively]. There was a positive correlation of M with <jats:italic>β</jats:italic>-<jats:sc>d</jats:sc>-glucan (<jats:italic>r</jats:italic>=0.28, <jats:italic>P</jats:italic>=0.01). The first positive M test was found up to a mean±<jats:sc>sd</jats:sc> of 8.8±8.5 (range 2–23) days prior to a clinical/mycological diagnosis of IC. Day-to-day variation in quantitative M levels was high. High-level AM responses were delayed until leucopenia resolved. The low specificities of the test performance may have been due to some of the comparator patients having subclinical <jats:italic>Candida</jats:italic> infections as evidenced by the high incidence of colonization among them (60 % had a colonization index of ≥0.5). The high NPVs suggest that the tests may be particularly useful in excluding IC. It is feasible to explore the use of serial measurements of M and AM as part of a broader diagnostic strategy for selecting PFN patients to receive antifungal drug therapy.</jats:p>