Development of Highly Sensitive Quantitative HBsAg Reagent and Its Availability

HBsAg is an envelope surface protein of the hepatitis B virus, and a marker of hepatitis B infection. In Japan, an HBsAg reagent was adopted as a blood screening test by the Japan Red Cross in 1972. Furthermore, a highly sensitive HBsAg reagent has been in use since 2008. Blood screening with HBsAg reagent use has contributed to a decrease in hepatitis B infections following blood donation. From the year 2000, the HBsAg reagent requirements have changed according to the progress in hepatitis B treatment. Serum levels of HBsAg and their temporal changes over long periods are used to understand a patient's clinical state and the effect of nucleoside analogue treatment. In 2013, we developed a highly sensitive quantitative chemiluminescent enzyme immunoassay (HBsAg-HQ) for HBsAg. Characteristics of the HBsAg-HQ reagent include the use of a pretreatment mixture and anti-HBs antibodies for the inner portion of HBsAg. The detection limit of HBsAg-HQ reagent (zero +3SD) is 0.0006 IU/mL, and the quantitative limit below 10% of the CV is 0.002 IU/mL. Therefore, we configured the measurement range from 0.005 to 150 IU/mL. Diagnostic sensitivity was tested for 10 seroconversion panels with HBsAg-HQ, and HBsAg-HQ yielded the same or higher sensitivity than other immunoassay products. In the report of Wai-Kay Seto et al., 25.8% of HBV patients whose sera were classified as HBs seroclearance by CLIA HBsAg reagent were judged as positive using our HBsAg-HQ reagent. Furthermore measurement of HBsAg levels is recommended to confirm the effect of nucleoside analogue treatment for chronic hepatitis patients or assessing the clinical condition before immunosuppression therapy for rheumatoid patients based on the guidelines of "The Japan Society of Hepatology" and "Japan College of Rheumatology". HBsAg qualitative reagents with high sensitivity are thus desirable for use in monitoring HBsAg.