Correlation between galactomannan antigen levels in serum and neutrophil counts in haematological patients with invasive aspergillosis

The detection of circulating galactomannan (GM) in serum samples is an important step in the diagnosis of invasive aspergillosis (IA). The assay has been mainly explored in neutropenic patients, and is now used to monitor patients at high risk for IA. However, the performance of the assay varies greatly among studies. The objective of this study was to explore the impact of the neutrophil count on the GM serum index at the time of IA diagnosis. Ninety-nine episodes of proven or probable, microbiologically documented IA in 91 patients with haematological malignancies were studied retrospectively. Three groups were identified: groups 1–3, with <100 polymorphonuclear neutrophils (PMN)/mm3 (n = 18), between 100 and 500 PMN/mm3 (n = 21), or >500 PMN/mm3 (n = 60), respectively. The mean GM index was significantly higher in group 1 than in the other groups (p <0.05). This finding did not change after stratifying the analysis with regard to the use of antibiotics likely to give false-positive GM results or with regard to treatment effective against fungi before the diagnosis of IA. This finding could be considered in the routine use of the GM antigenaemia test in non-neutropenic patients; a negative result or a low GM index should not eliminate the diagnosis of IA. This limitation calls for other microbiological tests, including analysis of bronchoalveolar lavage fluid, to establish a definitive diagnosis of IA.