A spergillus galactomannan (GM) detection in bronchoalveolar lavage (BAL) fluid samples is an important microbiologic criterion for diagnosing invasive pulmonary aspergillosis (IPA) in at-risk patients and is routinely performed in many clinical microbiology laboratories.Viscous respiratory specimens are often pretreated with a mucolytic agent for more homogeneous distribution of pathogens in the sample according to best practice recommendations for diagnosing fungal infections (1). Moreover, liquefaction of samples is a prerequisite for automated handling by streaking robots that are being used increasingly in microbiology labs. In addition, liquefaction of viscous BAL fluid samples might be necessary for the GM enzyme-linked immunosorbent assay (ELISA) (Platelia Aspergillus enzyme immunoassay; Bio-Rad Laboratories, Marnesla-Coquette, France) itself as it involves pipetting of the specimen. As reported previously, pretreatment of BAL fluid with Sputasol (Oxoid Microbiological Products, Basingstoke, England), a dithiothreitol-based mucolytic, significantly reduces GM levels (2). This prompted us to evaluate the influence of the Copan SLsolution, (Copan Italia SPA, Brescia, Italy), a commercially available, dithiothreitol-based, ready-to-use mucolytic agent, on GM levels.To study this, we reanalyzed GM-positive BAL fluid samples (both fluid and viscous), pretreated with SLsolution. We thawed 33 BAL fluid samples that, on initial testing, had a GM optical density index higher than or equal to 0.7 and had been stored at Ϫ20°C for 2 weeks to 16 months. Five out of 33 samples were obtained from patients with proven IPA, 10 were from patients with probable IPA, and 18 were from patients with no IPA, according to the revised definitions of the EORTC/MSG group (3). All samples were diluted at a 1:1 ratio with saline on the one hand and SLsolution on the other hand. All diluted samples were left to stand at room temperature for 15 to 30 min and thoroughly mixed with a vortex mixer. Pretreated samples that could not be tested immediately were stored in the refrigerator for 1 to 20 h. All sample pairs were analyzed in the same batch using the commercially available Platelia Aspergillus enzyme immunoassay for GM (Bio-Rad Laboratories).GM levels (optical density index) were generally lower in the saline group with a median of 1.7, compared to the original sample group with a median of 3.3, most likely due to the 1:1 dilution step (Table 1). The results of the original samples, however, correlated well with those of the saline-diluted samples (Spearman's rho, 0.636; P Ͻ 0.001). In contrast, dilution with SLsolution reduced all GM optical density indices to 0.3 or lower, with a median of 0.0, and thus led to a negative GM test result in all samples.Our findings confirm earlier observations from a similar study evaluating the effects of Sputasol pretreatment. Our results are highly relevant to clinical laboratories and stress the need to validate the use of mucolytic agents for pretreatment of samples for all tests that may be ...
