Evaluation of a (1->3)-beta-D-glucan assay for diagnosis of invasive fungal infections

Abstract

The Fungitell assay (Associates of Cape Cod, Inc.) is a commercial test that detects (1-3)-beta-D-glucan (BG) and is intended for diagnosis of invasive fungal infections. To evaluate the Fungitell assay, we tested serum and plasma samples from healthy blood donors and from patients with blood cultures positive for yeast or bacteria. All 36 blood donors were BG negative, and 13 of 15 candidemic patients were BG positive. Of 25 bacteremic patients, 14 (10 with gram-positive bacteremia) were BG positive. One of the latter patients with Staphylococcus aureus bacteremia also had invasive candidiasis, based on histological findings in a tissue biopsy; therefore, the BG result was a true positive. The sensitivity, specificity, and positive and negative predictive values of the Fungitell assay, by patient, for these three groups were 93.3%, 77.2%, 51.9%, and 97.8%, respectively. We also performed the Fungitell assay on sera that had been tested for Aspergillus galactomannan or Histoplasma antigen. All six Histoplasma antigen-positive patients and 31 of 32 Aspergillus galactomannan-positive patients were also BG positive. BG results for the 10 Histoplasma antigen-negative and the 32 Aspergillus galactomannan-negative patients varied, but we were unable to confirm many of the results. Between-run coefficients of variance (CVs) for the assay ranged from 3.2% to 16.8%; within-run CVs were < or =4.8%. The correlation coefficient for an interlaboratory reproducibility study was 0.9892. Concentrations of hemoglobulin, bilirubin, and triglycerides that caused 20% interference were 588, 72, and 466 mg/dl, respectively. Our results suggest that the Fungitel assay may be most useful for excluding invasive fungal infection.

FIG. 1.

Range of BG values for patient groups measured by the Fungitell assay. (A) The highest BG concentration for each patient is plotted for each patient group. Numbers indicating the highest BG value within each group are shown. Horizontal bars indicate the median value for each group. (B) Samples of ≤200 pg/ml are shown for each patient group. Horizontal lines indicate the cutoff for positive (>80 pg/ml) and negative (<60 pg/ml) samples. Patient groups are as follows: 1, healthy adult blood donors; 2, patients with blood cultures positive for yeast (8 patients with Candida albicans, 3 with Candida glabrata, 2 with Candida rugosa, 1 with Candida parapsilosis, and 1 with Candida lusitaniae); 3A, patients with blood cultures positive for gram-negative bacteria (1 with Klebsiella pneumoniae, 1 with Klebsiella oxytoca, 4 with Escherichia coli, 1 with Salmonella species, 2 with Pseudomonas aeruginosa, and 1 with Enterobacter cloacae); 3B, patients with blood cultures positive for gram-positive bacteria (9 with Staphylococcus aureus, (3 with coagulase-negative staphylococci, 1 with Streptococcus mitis, 1 with Streptococcus pneumoniae, and 1 with Enterococcus faecium); 4A, patients who were Histoplasma antigen positive (n = 6); 4B) patients who were Histoplasma antigen negative (n = 10); 5A, patients who were Aspergillus galactomannan positive (n = 32); and 5B, patients who were Aspergillus galactomannan negative (n = 32).

FIG. 2.

Interference plots showing the effects of increasing concentrations of hemoglobulin, bilirubin, and triglycerides on the Fungitell assay. The plots show percent inhibition of a BG-positive serum sample as a function of increasing concentrations of hemoglobin (A), bilirubin (B), and triglycerides (C).