[Non-specific reactions in four methods measuring (1-->3)-beta-D-glucan levels in plasma]

We detected non-specific reactions in the measurement of (1-->3)-beta-D-glucan levels (beta-glucan) in plasma, and the influences of the non-specific reactions on sensitivity and specificity of measurement methods were examined. In this study, 460 plasma samples from 174 patients at Kawasaki Medical School Hospital were used, and the plasma beta-glucan levels were measured by different four methods. The methods included the dilution-heating-endpoint (DHE), dilution-heating-turbidimetric (DHT), alkaline-kinetic (AK), and alkaline-endpoint method (AE) with and without 4-amidinophenyl benzoate hydrochloride (APB) of a protease inhibitor blocking the Limulus reaction. Non-specific reactions were detected from the calculated value under conditions with APB. Therefore, both of the actual values and the values equivalent to non-specific reactions were calculated. The incidence of non-specific reactions was 2.4% in DHE method, 0% in DHT, 53.3% in AK, and 99.3% in AE. The sensitivity and specificity in the methods were 35.7% and 96.0%, 28.6% and 96.0%, 78.6% and 80.1%, and 57.1% and 84.1%, respectively. When subtracted the non-specific reaction values from the actual values in AK and AE method, the specificity was increased by 91.4% and 94.0%, respectively. In these two methods, the non-specific reaction was considered to be a major cause of the low specificity. Finally, to measure plasma beta-glucan levels accurately, non-specific reactions should be excluded as possible by further improvement of measurement methods.