Antibody Screening
Screening for rubella antibody
Frequency of testing
It is likely that, given the low incidence of rubella in the UK, the cost benefit of the current rubella antibody screening strategy will be reviewed by the National Screening Committee.
The advice regarding frequency of testing given in Immunisation against Infectious Disease (The Green Book) ( 4) is appropriate. This advice states "Women should be screened for rubella antibodies at least in the first pregnancy, irrespective of a previous positive rubella antibody result. Very occasionally, laboratory errors or errors during reporting may result in patients who are rubella antibody negative being reported as rubella antibody positive. When there are documented results available of two tests using a specific method, both confirming the presence of rubella antibody, then further screening in pregnancy is unnecessary unless contact with suspected rubella or a rubella-like rash occurs."
This guidance does update the above advice, however, in recommending that further testing is not required if contact with suspected rubella or rubella-like rash occurs ( The risk of different rash illnesses in pregnancy ).
Health Authorities (HA) and NHS Trusts are recommended to review their compliance.
It is appreciated, however, that a pragmatic balance has to be drawn locally on the basis of cost efficiency between screening every woman in every pregnancy against a selective screening based on documented results .
Laboratory guidance
A number of reliable and validated assays are available for rubella antibody screening, such as enzyme-linked immunosorbent assays (EIA), radial haemolysis (RH), and latex agglutination (LA). The cut-off concentration of 15 international units (iu)/ml traditionally used in the UK was based on the lack of specificity of the haemagglutination inhibition (HI) test at low concentration of antibody. Many commercial EIAs have a cutoff of approximately 10 iu/ml and such a cut-off may be accepted as valid, providing the assay is continuously monitored by the use of a second confirmatory assay, as described below. This has been endorsed in the USA (36).
Sera giving
Given the sensitivity and specificity of EIA, RH and LA, if rubella-specific IgG can be detected by repeat testing in a validated assay or in two or more validated assays at whatever the concentration, the woman should be reported as "Rubella antibody detected". This approach would result in almost all those screened being reported as "Rubella antibody detected", or "Rubella antibody NOT detected" with advice being given "Rubella immunisation advised (post-delivery if pregnant)".
There may be exceptionally rare instances where further reference testing may be indicated, for example where variable results are obtained on retesting, and where there is a documented history of multiple doses of vaccine yet rubella-specific IgG cannot be detected on local testing.
If rubella-specific IgG is not detected, yet the woman has received two or more documented doses of rubella vaccine, further doses of vaccine are unlikely to be of value and protection against primary rubella assumed, although such women should be advised to report any rash illness.
Parvovirus B19 antibody screening
Unselected screening of pregnant women for past infection with parvovirus B19 is not recommended as no vaccine or prophylaxis are available. This advice will need reconsideration if a licensed vaccine becomes available.
