Letter: Prevention of post-transfusion hepatitis

Status and significance of testing for hepatitis B surface antigen and surface antibody

Following Blumberg's discovery of hepatitis B surface antigen (HBsAg), many attempts have been made to develop several in vitro diagnostic techniques for the detection of this antigen and its homologous antibody. The two-dimensional micro-Ouchterlony immunodiffusion has been the first technique used, rapidly replaced by procedures of increasing sensitivity characterized as second-generation and the currently available third-phase tests which include radioimmunoassay (RIA), reverse passive haemagglutination (RPHA), reverse passive latex agglutination (RPLA) and enzyme immunoassay (EIA). Among these, RIA appears to be the most sensitive and specific, whereas EIA, RPHA and RPLA have the advantage of long shelf-life of stable reagents, no need for sophisticated and expensive equipment and no hazard associated with the handling of radioactive isotopes. Moreover, the sensitivity of EIA should increase by objective reading with a colorimeter. The most sensitive method for the detection of surface antibody (anti-HBs) is again RIA, whereas passive haemagglutination (PHA) had the advantage of providing titres. Finally EIA, based on inhibition of a known amount of HBsAg, has at least the same sensitivity as PHA, but has the advantage that reagents are more stable and that it permits screening for both HBsAg and anti-HBs with the same reagents at the same time. The application of these highly sensitive techniques for the detection of HBsAg and anti-HBs has resulted in a consistent reduction in the incidence of post-transfusion hepatitis type B and in a better understanding of the aetiology, epidemiology and natural history of this infection.

Which techniques should be used to screen blood donations for hepatitis B surface antigen?

Preservation of all donor sera already tested for Hepatitis B surface antigen (HBsAg) by counterimmunoelectrophoresis (C.I.E.P.) allowed C.I.E.P., reversed passive haemagglutination (R.P.H.A.), and radioimmunoassay (R.I.A.) to be evaluated as screening techniques. Out of 165 811 donors tested for the first time 207 were found by C.I.E.P. to be positive for HBsAf-a prevalence of 0-12%. At the next donation 10 of those apparently negative on first screening were HBsAg positive by C.I.E.P., and nine of these were shown by retesting with R.P.H.A. and R.I.A. to have been positive at the earlier donation. These nine false negatives caused four cases of transfusion-transmitted HBsAg-positive hepatitis. On comparative screening of 22 239 donations C.I.E.P. detected 27 sera positive for HBsAg, R.P.H.A. 39, and R.I.A. 41. Thus R.I.A. increased the detection rate by more than half over C.I.E.P. From these 14 further false-negative donations by C.I.E.P. six cases-one fatal-of HBsAg-positive hepatitis occurred. The number of false positive reactions when using R.P.H.A. or R.I.A. for screening was less than 1%. As many as 700 donations in one day have been tested by R.P.H.A. or R.I.A. R.P.H.A. is faster and less expensive than R.I.A., but R.I.A. is more objective. Either R.P.H.A. or R.I.A. should replace C.I.E.P. as the routine method of screening donor sera for HBsAg.