(1→3)-β-d-Glucan (BDG) is a polysaccharide glucose polymer that is a constituent of the cell walls of many pathogenic fungi; detection of this compound in the peripheral blood with serum assay is important in the diagnosis of invasive fungal infections (with the notable exceptions of
Mucorales and cryptocci, which release little to no BDG that can be detected on current serum assays). The measurement of BDG levels is based on the
Limulus test-namely, factor G is a protease zymogen found in
Limulus amoebae extracted from horseshoe crab species, which then reacts with BDG to initiate a coagulation cascade, and activity of this reaction is quantified using various analytic chemistry methods. Unfortunately, false-positive results can be a limiting factor in the usefulness of BDG assays-the assay may indeed be detecting BDG for reasons other than invasive fungal infection. BDG assays can be positive in people undergoing hemodialysis with cellulose membranes, being treated with blood products that have been filtered through cellulose depth filters containing BDG (such as immunoglobulin and albumin), with serosal exposure to glucan-containing gauze, or the administration of certain antibiotics that are either derived from fungal agents (such as ampicillin-clavulanic acid) or manufactured using a process involving cellulose filters that leach into the product. There have also been case reports of bacteremia interfering with the accuracy of BDG assays, although this has not been consistently characterized.
BDG assay is a valuable tool in helping to diagnose invasive fungal infections, but assays should be performed and interpreted in the proper clinical context; particularly for an unexpectedly positive assay, the possibility of a false-positive result should be considered.
References: Reactivity of (1–>3)-beta-d-glucan assay with commonly used intravenous antimicrobials.
References: Detection of high serum levels of β-D-Glucan in disseminated nocardial infection: a case report
