What laboratory tests are available to confirm a diagnosis of rubella, and how should I interpret the results?

Laboratory tests available to confirm rubella diagnosis:

• Serological testing for rubella-specific IgM and IgG antibodies is the primary method to confirm rubella infection. Detection of rubella IgM antibodies indicates recent infection, while IgG antibodies indicate past exposure or immunity.
• Oral fluid samples may be collected immediately for rubella virus detection; if positive, further confirmatory testing and genotyping can be performed.
• In pregnant women, laboratory investigation is mandatory regardless of immunization status or previous testing, to confirm rubella infection and guide management.

Interpretation of results:

• A positive rubella IgM test confirms recent rubella infection.
• Presence of rubella IgG without IgM usually indicates immunity from past infection or vaccination.
• In pregnancy, confirmation of rubella infection requires urgent referral for fetal risk assessment, especially if infection occurs before 20 weeks gestation.
• Negative serology in a pregnant woman with rash-like illness does not exclude rubella; other infections with similar presentations (e.g., parvovirus B19, measles) should be considered and tested.
• Laboratory confirmation is essential for surveillance and public health reporting but should not delay notification based on clinical suspicion.

All suspected cases must be reported immediately to the local Health Protection Team, and samples should be clearly labelled with pregnancy status if applicable. The Health Protection Team will advise on further testing and management. If rubella infection is confirmed in pregnancy, management depends on gestational age due to the risk of congenital rubella syndrome (CRS) being highest before 16 weeks gestation and negligible after 20 weeks.

There is no effective treatment to prevent CRS, and immunoglobulin is not routinely recommended post-exposure in pregnancy. Further diagnostic tests such as amniocentesis may be indicated in confirmed cases.

Laboratory confirmation in non-pregnant individuals is mainly for surveillance rather than individual management.

Notification should be based on clinical suspicion and not delayed awaiting laboratory confirmation.

Summary: Rubella diagnosis is confirmed by detecting rubella-specific IgM antibodies or viral RNA in oral fluid samples. Interpretation must consider pregnancy status and gestational age to guide urgent management and public health actions.

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