Frequent false-positive results of Aspergillus latex agglutination test: transient Aspergillus antigenemia during neutropenia.

BACKGROUND Two serologic assays, Aspergillus latex agglutination testing (LA) and plasma (1-->3)-beta-D-glucan (BDG) measurement, are used when invasive pulmonary aspergillosis (IPA) is suspected. Despite the high specificity of these assays, false-positive results are frequent for neutropenic patients. This study was conducted to evaluate the efficacy of LA and BDG and to investigate the cause of the false-positive results. METHODS Eighty-eight consecutive patients with hematologic malignancies who underwent intensive chemotherapy were tested weekly with LA and BDG. RESULTS Sixteen of 88 patients were diagnosed as having IPA. The sensitivity, specificity, and positive predictive values were 23%, 98%, and 64% for LA and 27%, 88%, and 52% for BDG, respectively. Of 11 patients who became positive for LA only during neutropenic periods, 2 patients developed IPA. In contrast, six of eight patients who became positive for LA during nonneutropenic periods developed IPA. Transient Aspergillus antigenemia was more frequently encountered during neutropenia (2.9%) than during nonneutropenic periods (0.2%). The plasma BDG concentration increased at the nadir of neutropenia in 36 of 45 patients who had no signs of IPA, and it exceeded the level of 20 pg/mL in 2 patients. CONCLUSIONS Both BDG and LA have a low sensitivity and a high specificity for IPA. However, the false-positive rate of LA increases during neutropenic periods. Caution should be exercised in interpreting the results of these blood tests, especially when patients are neutropenic.