[A discrepancy in the values of serum (1-3)-beta-D-glucan measured by two kits using different methods]

Development of a Highly Sensitive β-Glucan Detection System Using Scanning Single-Molecule Counting Method

To overcome the limitations of the Limulus amebocyte lysate (LAL) assay method for the diagnosis of invasive fungal infection, we applied a reaction system combining recombinant β-glucan binding proteins and a scanning single-molecule counting (SSMC) method. A novel (1→3)-β-D-glucan recognition protein (S-BGRP) and a (1→6)-β-glucanase mutant protein were prepared and tested for the binding of (1→6)-branched (1→3)-β-D-glucan from fungi. S-BGRP and (1→6)-β-glucanase mutant proteins reacted with β-glucan from Candida and Aspergillus spp. Although LAL cross-reacted with plant-derived β-glucans, the new detection system using the SSMC method showed low sensitivity to plant (1→3)-β-D-glucan, which significantly improved the appearance of false positives, a recognized problem with the LAL method. Measurement of β-glucan levels by the SSMC method using recombinant β-glucan-binding proteins may be useful for the diagnosis of fungal infections. This study shows that this detection system could be a new alternative diagnostic method to the LAL method.

Clinical viability of Fungitell, a new (1→3)-β-D: -glucan measurement kit, for diagnosis of invasive fungal infection, and comparison with other kits available in Japan

Fungitell, a (1→3)-β-D: -glucan (β-D: -glucan) measurement kit, was approved in the United States in 2004. Three other kits for measurement of β-D: -glucan, Fungitec G test MK (G-MK), β-Glucan test Wako (Wako), and β-Glucan test Maruha (Maruha), are commonly used for diagnosis of invasive fungal diseases in Japan. We evaluated the clinical viability of the Fungitell kit and compared it with the 3 kits generally used in Japan. The plasma β-D: -glucan values measured with each kit showed some differences, possibly because different β-D: -glucan standards, blood pretreatment methods, and kinds of horseshoe crab (a raw material for the main reagent) are used in each kit. Measures of diagnostic efficiency, for example the sensitivity, specificity, and positive and negative predictive values, varied among the kits. Although the areas under the receiver operating characteristic curves of the kits were not significantly different, the sensitivity of the Fungitell kit was the highest, followed by that of the G-MK kit. The sensitivity of the Wako and Maruha kits was low, but the specificity of these tests was higher than that of the G-MK or Fungitell kits. These inconsistent β-D: -glucan measurements could interfere with diagnosis of invasive fungal infection. Early establishment of an international standard method for measurement of β-D: -glucan is required.

Preemptive therapy in nonneutropenic patients with Candida infection using the Japanese guidelines

BACKGROUND

The Japanese Guidelines for the Diagnosis and Treatment of Deep-Seated Mycosis were established in 2003. Proven Candida infection (CI) is defined as at least one positive blood culture yielding a Candida species. Clinically documented CI requires documentation of more than 2 sites of colonization and a positive plasma beta-D-glucan test. Possible CI is diagnosed by one of the above criteria in febrile, nonneutropenic critically ill patients.

OBJECTIVE

To assess the use of definitions of clinically documented and possible CI for guiding preemptive antifungal therapy in critically ill patients.

METHODS

The patients treated in our intensive care unit (ICU) for at least 48 hours between 2000 and 2004 were investigated. The administration of antifungal agents and ICU mortality were compared among proven, clinically documented, and possible CI groups for age, sex, APACHE II score, diagnosis, length of ICU stay, treatment, number of colonization sites, and plasma beta-D-glucan level.

RESULTS

Six patients were diagnosed with proven CI, 25 were diagnosed with clinically documented CI, and 104 with possible CI. The patients with clinically documented CI were compared with those with possible CI, and statistically significant differences were found in the following variables: APACHE II score (p = 0.018), length of ICU stay (p < 0.01), use of ventilator (p = 0.027), tracheotomy (p = 0.027), number of colonization sites (p < 0.001), plasma beta-D-glucan level (p < 0.001), and administration of antifungal agents (p < 0.001); incidence of mortality was not statistically significant (p = 0.33). The shorter length of ICU stay, use of ventilator, and continuous hemodiafiltration were risk factors for death after adjusting for APACHE II score, admission before/after 2003, antifungal therapy, and other factors. Although the frequency of the administration of preemptive antifungal therapy was higher after 2003 than before, the mortality rate did not differ significantly.

CONCLUSIONS

The use of the definitions of clinically documented and possible CI may be beneficial for determining when it is appropriate to initiate preemptive antifungal therapy. However, use of the guidelines did not lead to prevention of possible CI proceeding to clinically documented CI or to improved mortality.

Contribution of (1->3)-beta-D-glucan chromogenic assay to diagnosis and therapeutic monitoring of invasive aspergillosis in neutropenic adult patients: a comparison with serial screening for circulating galactomannan

Two noninvasive diagnostic tests, (1-->3)-beta-D-glucan (BG) (Glucatell) and galactomannan (GM) (Platelia Aspergillus), were used retrospectively in a twice-weekly screening for the diagnosis of invasive aspergillosis (IA) in 40 treatment episodes (one hospital visit per patient) in 40 neutropenic adult patients at high risk for IA. Five proven IA cases, three probable IA cases, and three possible IA cases were diagnosed. Diagnostic levels of both BG and GM were detected in 100% of patients with proven IA cases and in 66% of patients with probable IA cases. The kinetics of both markers in patients with IA were similar. The sensitivity, specificity, and positive and negative predictive values for GM and BG were identical, namely, 87.5, 89.6, 70, and 96.3%, respectively. False-positive reactions occurred at a rate of 10.3% in both tests, but the patients showing false-positive results were different in each test. Both tests anticipated the clinical diagnosis, computed tomography abnormalities, and the initiation of antifungal therapy in most patients, but BG tended to become positive earlier than GM. A combination of the two tests improved the specificity (to 100%) and positive predictive value (to 100%) of each individual test without affecting the sensitivity and negative predictive values. In conclusion, BG and GM detection are useful tests for the diagnosis of IA in high-risk hematological patients, but a combination of the two tests was very useful to identify false-positive reactions by each test.

Prospective comparison of the diagnostic potential of real-time PCR, double-sandwich enzyme-linked immunosorbent assay for galactomannan, and a (1-->3)-beta-D-glucan test in weekly screening for invasive aspergillosis in patients with hematological disorders

The establishment of an optimal noninvasive method for diagnosing invasive aspergillosis (IA) is needed to improve the management of this life-threatening infection in patients with hematological disorders, and a number of noninvasive tests for IA that target different fungal components, including galactomannan, (1-->3)-beta-d-glucan (BDG), and Aspergillus DNA, have been developed. In this study, we prospectively evaluated the diagnostic potential of three noninvasive tests for IA that were used in a weekly screening strategy: the double-sandwich enzyme-linked immunosorbent assay (ELISA) for galactomannan (Platelia Aspergillus), a real-time PCR assay for Aspergillus DNA (GeniQ-Asper), and an assay for BDG (beta-glucan Wako). We analyzed 149 consecutive treatment episodes in 96 patients with hematological disorders who were at high risk for IA and diagnosed 9 proven IA cases, 2 probable IA cases, and 13 possible invasive fugal infections. In a receiver-operating characteristic (ROC) analysis, the area under the ROC curve was greatest for ELISA, using two consecutive positive results (0.97; P = 0.036 for ELISA versus PCR, P = 0.055 for ELISA versus BDG). Based on the ROC curve, the cutoff for the ELISA could be reduced to an optical density index (O.D.I.) of 0.6. With the use of this cutoff for ELISA and cutoffs for PCR and BDG that give a comparable level of specificity, the sensitivity/specificity/positive predictive value/negative predictive value of the ELISA and the PCR and BDG tests were 1.00/0.93/0.55/1.00, 0.55/0.93/0.40/0.96, and 0.55/0.93/0.40/0.96, respectively. In conclusion, among these weekly screening tests for IA, the double-sandwich ELISA test was the most sensitive at predicting the diagnosis of IA in high-risk patients with hematological disorders, using a reduced cutoff of 0.6 O.D.I.