The Plasma (1→3)-β-D-glucan Assay, a Japanese Contribution to the Diagnosis of Invasive Fungal Infection

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.