Fungitell (1,3)-B-D-Glucan
Fungitell, which measures (1–3)-?-D-glucan in serum, has received FDA approval for use as an adjunct in the diagnosis of invasive fungal infections. Fungal cell walls are primarily composed of polysaccharides such as glucan, chitin, and mannan. Glucan is the major constituent of the cell walls of most pathogenic and saprophytic fungi, with the notable exception of the Zygomycetes such as Mucor and Rhizopus. Likewise, Cryptococcus produces only low levels of ?-D-glucan and Blastomyces dermatitidis produces very little in the yeast/tissue phase.
A meta-analysis of ?-D-glucan cites pooled sensitivity and specificity of Fungitell for the diagnosis of an invasive fungal infection as 71% and 82%, respectively (CID 2011:52, 15 March). Fungitell may be useful for detection of ?-D-glucan production from fungal pathogens including Candida, Aspergillus, Fusarium, and Histoplasma. Serum from normal subjects contains low levels of detectable ?-D-glucan (<40 pg/mL) likely due to the presence of commensal Candida species in the gastrointestinal tract. Serum (1-3) ?-D-glucan levels of 60-79 pg/mL are considered indeterminate, while results >80 pg/mL are indicative of a possible invasive fungal infection.
Fungitell results are best interpreted with consideration of its limitations. False-positive results have been attributed to concomitant bacterial infections (especially Streptococcus), exposure to hemodialysis cellulose membranes, and infusion of intravenous immunoglobulin or albumin. Furthermore, surgery patients exposed to glucan-containing sponges or gauze may have elevated levels for 3-4 days post-operatively. False negative reactions are associated with lipemic specimens, hemolyzed specimens and infections with fungi that lack significant levels of (1–3)-?-D-glucan such as Zygomycetes (Mucor, Rhizopus, and Absidia), Cryptococcus species, and Blastomyces dermatitidis.
Serum (1–3)-?-D-glucan concentrations decrease within two weeks after initiation of anti-fungal therapy in patients who are responding to therapy. A continuous increase in serum (1–3)-?-D-glucan concentrations is seen in patients not responding to antifungal treatment. Once-weekly testing is recommended to assess response to treatment.
Specimen requirement is 3 to 5 mL of blood collected into a red top tube of blood with or without a serum separator gel. The original sample, not a pour-off tube, should be submitted to decrease the likelihood of false-positive results due to environmental contamination.
