Detection of hepatitis B surface antigen in potentially contaminated human plasma and plasma fractions

A new method is described for the quantitative detection of HBsAg in whole human plasma and in plasma fractions. The nonantigen proteins are digested with pepsin at low pH, and the antigen is precipitated with PEG. With use of only 20 ml of contaminated plasma, as few as 5.0 x 10(6) HBsAg particles/ml can be detected--a 40-fold increase in the apparent level of sensitivity of the Ausria II RIA (2.0 x 10(8) particles/ml). With 500 500 ml or more of plasma or plasma fractions, fewer than 5.0 x 10(5) particles/ml can be assayed--a 400-fold increase in RIA sensitivity and 1/10 the antigen concentration found in sera that proved infective when injected into chimpanzees. The pepsin-PEG method was used to quantitate the particles per milliliter in four equivocal RIA samples from the NIH Bureau of Biologics, three of which were definitely shown to contain antigen. The method has also been employed to detect fewer than 2.0 x 1010(8) particles/ml of HBsAg in deliberately contaminated high purity AHF concentrates and may be useful for monitoring plasma fractions prepared on a large scale or for detecting the antigen in equivocal samples from blood banks.