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[The Plasma (1→3)-β-D-glucan Assay, a Japanese Contribution to the Diagnosis of Invasive Fungal Infection]
1Medical Laboratory, Higashi Saitama General Hospital.
Abstract:
In 1985, a (1→3)-β-D-glucan assay based on the discovery of a (1→3)-β-D-glucan-sensitive coagulation factor in the horseshoe crab amebocytes was developed in Japan, as a test aid in the diagnosis of invasive fungal infections. After many clinical trials, it has now been incorporated in practice guidelines both in Japan and abroad for the diagnosis and management of invasive fungal infection, and is now available worldwide. In Japan, however, two commercial kits that differ widely in sensitivity to (1→3)-β-D-glucan are used; namely, the colorimetric and the turbidimetric assays. Thus, attention must be paid when comparing measurement values between the two tests. In most cases, one pg/ml of the latter corresponds to about 7 pg/ml of the former. This raises the cutoff value of the turbidimetric assay far higher than that of the colorimetric assay, raising concern about missing many true cases of invasive fungal infections. The detection limit of the turbidimetric method is equivalent to as high as 60 pg/ml if converted to the colorimetric measurement. Thus, early diagnosis will be difficult to make based on detection of a rise in the β-D-glucan level in the lower range of concentration. The kits used overseas also differ in sensitivity; thus, global standardization or harmonization will be required to establish inter-assay data comparability and to enhance the usefulness of the tests. In the future, genetic engineering may provide an alternative source of the coagulation pathway enzymes other than the horseshoe crabs, in accordance with the global trends in animal protection, and bring about new opportunities for standardization.
Insights
The (1→3)-β-D-glucan assay aids invasive fungal infection diagnosis. However, differing kit sensitivities, particularly in Japan, may lead to missed diagnoses, necessitating global standardization for reliable results.
Area of Science:
- Clinical diagnostics
- Mycology
- Biochemistry
Background:
- The (1→3)-β-D-glucan assay, developed in Japan in 1985, utilizes horseshoe crab amebocytes to detect fungal infections.
- It is now a globally recognized diagnostic aid for invasive fungal infections, included in international practice guidelines.
- Two distinct commercial assay kits, colorimetric and turbidimetric, are prevalent in Japan, exhibiting significant differences in sensitivity.
Purpose of the Study:
- To highlight the critical differences in sensitivity between colorimetric and turbidimetric (1→3)-β-D-glucan assays.
- To address concerns regarding the potential for missed diagnoses due to assay variability.
- To advocate for global standardization of (1→3)-β-D-glucan testing methods.
Main Methods:
- Comparison of measurement values and sensitivity between colorimetric and turbidimetric (1→3)-β-D-glucan assay kits.
- Analysis of detection limits and cutoff values for each assay type.
- Review of clinical trial data and practice guideline incorporation.
Main Results:
- A significant sensitivity disparity exists: 1 pg/ml in turbidimetric assays often equates to approximately 7 pg/ml in colorimetric assays.
- The turbidimetric assay's higher cutoff value and detection limit (equivalent to 60 pg/ml colorimetric) raise concerns about missing low-concentration infections.
- Variability in kit sensitivity is also observed internationally, impacting inter-assay data comparability.
Conclusions:
- The differing sensitivities of commercial (1→3)-β-D-glucan assays, especially in Japan, pose a risk of underdiagnosing invasive fungal infections.
- Global harmonization and standardization of these assays are crucial for accurate diagnosis and effective patient management.
- Future developments, including genetic engineering for enzyme sources, may offer new avenues for standardization and animal welfare.
