There have been conflicting reports of false positive
galactomannan assay results in patients with systemic
cryptococcosis. We sought to determine the frequency of GM positivity in patients with pulmonary
cryptococcosis and confirm the source of this cross-reactivity in vitro. We conducted a retrospective study to elucidate the rate of
galactomannan (GM) false positivity and cause in a cohort of 29 patients with pulmonary cryptococcal disease. The production of GM cross-reacting substances by clinical isolates and laboratory isolates of C. neoformans was tested in vitro. The mean serum GM index (Platelia Aspergillus) in patients with pulmonary
cryptococcosis was 1.06, with 16 (55.2%) of patients having values above the positive cutoff value of 0.5. GM index values significantly decreased
after treatment of
cryptococcosis. There was no significant correlation between
galactomannan and cryptococcal
glucuronoxylomannan antigen (Eiken
Latex test) results. Culture supernatants from clinical isolates and wild-type C. neoformans did not react in the GM assay; however, growth in the presence of 6%
sodium chloride induced the production of cross-reacting GM
antigens in culture supernatants from clinical isolates, wild type and a
glucuronoxylomannan-deficient mutant of C. neoformans, but not in culture supernatants from a
galactoxylomannan-deficient strain. Our results support the cross-reactivity of cryptococcal
galactoxylomannan with the serum GM assay in vitro and in patients with pulmonary cryptococcal
infection.