D-index: A New Scoring System in Febrile Neutropenic Patients for Predicting Invasive Fungal Infections

OBJECTIVE: Neutropenia is a critical risk factor for invasive fungal infections (IFIs). We retrospectively performed this study to assess the performance of the D-index, a new test that combines both the duration and the severity of neutropenia, in predicting IFIs among patients with acute myelogenous leukemia. MATERIALS AND METHODS: Fifteen patients with IFIs and 28 patients who did not develop IFIs were enrolled in the study. The D-index was defined as the area over the neutrophil curve, whereas the cumulative-D-index (c-D-index) was the area over the neutrophil curve from the start of neutropenia until the first clinical manifestation of IFI. RESULTS: The D-index and the c-D-index tended to be significantly higher in patients with IFIs, with medians of 10,150 (range: 4000-22,000) and 5300 (range: 2300-22,200), respectively (p=0.037 and p=0.003, respectively). The receiver operating characteristic analyses showed that there was a cutoff point of 3875 for the D-index in predicting IFI; the sensitivity, specificity, and positive and negative predictive values were 100%, 67.9%, 35.4%, and 100%, respectively. There was also a cutoff point of 4225 for the c-D-index in predicting IFI; the sensitivity, specificity, and positive and negative predictive values for the c-D-index were 93.3%, 71.4%, 36.6%, and 98.4%. CONCLUSION: The D-index and especially the c-D-index could be useful tools with high negative predictive value to exclude as well as to predict IFIs in the management of neutropenic patients.