Clinical evaluation of two different (1,3)-ß-d-glucan assays for diagnosis of invasive fungal diseases: A retrospective cohort study

Developments in Fungal Serology

Purpose of Review

The true incidence of fungal disease is hampered by conventionally poor diagnostic tests, limited access to advanced diagnostics, and limited surveillance. The availability of serological testing has been available for over two decades and generally underpins the modern diagnosis of the most common forms of fungal disease. This review will focus on technical developments of serological tests for the diagnosis of fungal disease, describing advances in clinical performance when available.

Recent Findings

Despite their longevity, technical, clinical, and performance limitations remain, and tests specific for fungal pathogens outside the main pathogens are lacking. The availability of LFA and automated systems, capable of running multiple different tests, represents significant developments, but clinical performance data is variable and limited.

Summary

Fungal serology has significantly advanced the diagnosis of the main fungal infections, with LFA availability increasing accessibility to testing. Combination testing has the potential to overcome performance limitations.

Comparison of Three β-Glucan Tests for the Diagnosis of Invasive Candidiasis in Intensive Care Units

The (1→3)-β-d-glucan (BDG) is a marker of invasive fungal infection that can be detected in serum by different commercial kits. In this study, we compared the performance of the Fungitell assay (FA), the Fungitell STAT assay (STAT), and the Wako β-glucan test (WA) for the diagnosis of invasive candidiasis (IC) in the intensive care unit (ICU). Patients for whom at least one BDG testing was required for a clinical suspicion of IC were retrospectively enrolled. A total of 85 serum samples from 56 patients were tested by the three BDG tests. The rate of IC was 23% (13/56) with a predominance of noncandidemic (intra-abdominal) IC. STAT and WA results exhibited overall good correlation with those obtained by FA (Spearman's coefficient R = 0.90 and R = 0.89, respectively). For the recommended cutoffs of positivity, sensitivity and specificity for IC diagnosis were 77%/51% (FA, 80 pg/mL), 69%/53% (STAT, ratio 1.2), and 54%/65% (WA, 7 pg/mL), respectively. Optimal performance was obtained at 50 pg/mL (FA), ratio 1.3 (STAT), and 3.3 pg/mL (WA) with sensitivity/specificity of 85%/51%, 69%/57%, and 77%/58%, respectively. Overall, the three BDG tests showed comparable but limited performance in this setting with positive and negative predictive values for an estimated IC prevalence of 20% that were in the range of 30 to 35% and 85 to 95%, respectively.

The Comparative Evaluation of the Fujifilm Wako β-Glucan Assay and Fungitell Assay for Diagnosing Invasive Fungal Disease

Serum 1,3-β-d-glucan(BDG) is a broad fungal biomarker for invasive fungal disease (IFD). More data is still required to support the Fujifilm Wako assay as a valuable alternative to the widely used Fungitell assay. We included archived serum samples from 157 individuals (97 cases; 33-IA, 64-IC, and 60 controls) for the comparative performance evaluation of the Fungitell assay and the Fujifilm Wako assay for IFD diagnosis. The BDG value was significantly higher in patients with IFD vs. controls (70.79 pg/mL vs. 3.03 pg/mL, p: 0.0002). An area under the curve (AUC) for the IFD, IC, and IA diagnosis was 0.895, 0.910, and 0.866, respectively, for the Fujifilm Wako assay. Based on the highest Youden’s index (0.667), a cutoff of 5 pg/mL was selected as the optimum for the Fujifilm Wako assay with good sensitivity (79.4%), specificity (88.3%) and agreement (84.7%, Cohen’s k:0.691) with the Fungitell assay. The mean run-time of the Fujifilm Wako assay was 70.12 min, and real-time observation allowed earlier time to result in Fujifilm Wako vs. Fungitell assay (37 vs. 120 min, p: < 0.0001). Thus, our findings support the diagnostic value of the Fujifilm Wako assay for the diagnosis of IFD. However, there is still a need to validate diagnostic protocols to optimize their use in multi-centre studies with different patient groups.

A Negative (1,3)-β-D-Glucan Result Alone Is Not Sufficient to Rule Out a Diagnosis of Pneumocystis Pneumonia in Patients With Hematological Malignancies

Background: Serum (1,3)-β-D-glucan (BG) testing is increasingly being used in the diagnostic armamentarium for invasive fungal diseases. Given its high sensitivity, some studies suggest that a negative BG result contributes to rule out a diagnosis of Pneumocystis pneumonia (PCP). However, recent reports described a suboptimal sensitivity in HIV-negative immunocompromised patients. In this study, we evaluated the performance of BG assay for PCP diagnosis in HIV-negative patients with diverse PCP risk factors. We also assessed the correlation between Pneumocystis jirovecii load in pulmonary samples and serum BG levels.

Methods: We retrospectively included HIV-negative patients with microscopically proven PCP and for whom a BG result was available. We also enrolled patients colonized by Pneumocystis as control group. Colonized patients were matched with PCP patients based on their underlying condition that exposed to PCP. Pulmonary fungal loads were determined by an in-house real-time PCR, and BG levels were measured by using the Fungitell® kit (Associates of Cape Cod, Inc.).

Results: Thirty-nine patients were included in each of the two groups. Thirty-four of 39 PCP patients and one of 39 colonized patient had a positive BG test, resulting in a sensitivity of 0.87 (95% CI: 0.73–0.94), a specificity of 0.97 (95% CI: 0.87–0.99), a positive predictive value of 0.97 (95% CI: 0.85–0.99), and a negative predictive value of 0.88 (95% CI: 0.75–0.95) for BG assay. Nonetheless, median BG level differed according to the underlying condition. Among the PCP group, the lowest median level of 211 pg/ml was observed in patients with hematological malignancy (HM) and differed significantly from that observed either in solid organ transplants (3,473 pg/ml) or in patients with autoimmune or inflammatory disorder (3,480 pg/ml). Indeed, the sensitivity of BG assay was estimated at 0.64 (95% CI: 0.35–0.85) in HM patients and was lower than the one observed in the whole PCP group. Furthermore, BG level and fungal burden correlated poorly among all PCP patients.

Conclusion: BG is not a reliable biomarker for ruling out PCP in HIV-negative patients with HM. Interpretation of a negative BG result should take into account, but not be limited to, the underlying condition predisposing to PCP.

Prospective comparison of (1,3)-beta-D-glucan detection using colorimetric and turbidimetric assays for diagnosing invasive fungal disease

Serum (1→3)-β-D-glucan (BDG), an pan fungal antigen, is detected in some invasive fungal diseases (IFDs). We compared two commercial kits, the Fungitell assay (FA) (colorimetric) and the Wako assay (WA) (turbidimetric) over a 4-month period to prospectively test 171 patients who mainly had hematological conditions (62%) and experienced episodes (n = 175) of suspected invasive fungal infection. Twenty-three episodes due to BDG-producing fungi were diagnosed (pneumocystosis, n = 12; invasive aspergillosis, n = 5; candidemia, n = 3; invasive fusariosis, n = 2; hepato-splenic candidiasis, n = 1).Both assays provided similar areas under the curves (AUC = 0.9). Using the optimized positivity thresholds (≥120 pg/ml for FA and ≥ 4 pg/ml for WA), the sensitivity and specificity were 81.8% (CI95: 61.5-92.7), 94.8% (90.1-97.3) for FA and 81.8% (61.5-92.7), 95.4% (90.9-97.8) for WA. Negative predictive value was 97.3% (93.3-99.0) for both tests. If the manufacturer's positivity threshold (≥11 pg/ml) was applied, the WA sensitivity decreased to 50%. Among 71 patients with bacterial infections, 21.1% were FA-positive and 5.6% were WA-positive (p < 10-2).The WA performed similarly as compared to the FA with an optimized cutoff value. The WA is a single sample test that is clinically relevant when a prompt therapeutic decision is required.

LAY SUMMARY

Serum (1→3)-β-D-glucan testing is dominated by two kits including Fungitell colorimetric assay (FA) and the Wako turbidimetric assay (WA). We compared them prospectively and observed that they both perform similarly when selecting their optimal threshold (≥120 pg/ml for FA and ≥ 4 pg/ml for WA).

Protocol for the pBDG2 Study: Prospective Evaluation of 1.3-β-D-Glucan in the Peritoneal Fluid for the Diagnosis of Intra-Abdominal Candidiasis in Critically Ill Patients

Background: The delayed diagnosis of the presence of Candida in severe intra-abdominal infections exposes patients to an increased risk of mortality. The prevalence of intra-abdominal candidiasis (IAC) varies with the type of intra-abdominal infection, the underlying conditions and the presence of risk factors for Candida infection. This study aims to evaluate the interest of the measure of 1.3-β-D-glucan (BDG) in the peritoneal fluid for the early diagnosis of IAC. Methods and analysis: This is a prospective multicenter (n = 5) non-interventional study, focusing on all critically ill patients with an intra-abdominal infection requiring intra-abdominal surgery. The primary objective is to assess the diagnostic performance of the BDG measured in the peritoneal fluid for the early detection of IAC using the Candida culture as the gold standard. The secondary objective is to report the prevalence of IAC in the selected population. This study aims to enroll 200 patients within 48 months. By estimating the prevalence of IAC in the selected population at 30%, 50 patients with IAC (cases) are expected. These 50 IAC cases will be matched with 50 non-IAC patients (as a control group). The peritoneal BDG will be measured a posteriori in all of these 100 selected patients. This article presents the protocol and the current status of the study. Only the prevalence of IAC is reported as preliminary result.