Rubella IgM in Dehradun

What is a Rubella IgM?

IgM is the immune system's first-response antibody, appearing within days of a rubella infection and typically persisting for a few weeks to a couple of months, so its presence suggests infection now or very recently. That distinguishes it from IgG, which lasts a lifetime and indicates immunity. The reason this test carries such weight is confined almost entirely to pregnancy, where rubella acquired in the first trimester can cause congenital rubella syndrome, with deafness, cataracts, heart defects and developmental problems in the baby, and where the risk falls substantially as pregnancy advances. Outside pregnancy rubella is a mild self-limiting illness and testing is rarely needed. The essential caution is that a positive IgM must not be acted upon alone. False positives are well recognised, cross-reaction with other viral infections occurs, IgM can persist longer than expected, and it can also appear after recent vaccination. Confirmation involves repeating the test, measuring paired IgG levels, and often an IgG avidity test, which estimates whether the infection predates the pregnancy.

Why take this test?

Rubella IgM is advised in pregnancy where there has been a rash illness with fever, swollen lymph nodes behind the ears or at the back of the neck, or joint pains, and where documented contact with a confirmed rubella case has occurred. It is used alongside IgG so that the pair can be interpreted together, since prior immunity makes a genuine new infection most unlikely. It is also used in outbreak investigation and in a newborn with features suggesting congenital infection. It is not a routine antenatal screening test in women who are already known to be IgG positive and well, and ordering it speculatively produces false positives that cause serious and often unwarranted alarm in exactly the population least able to absorb it. Take any positive result straight to your obstetrician, who will arrange confirmatory testing before any conclusion is drawn.

• A rash illness with fever during pregnancy
• Swollen lymph nodes behind the ears or at the back of the neck
• Documented contact with a confirmed rubella case in pregnancy
• Joint pains with a rash in a pregnant woman
• A newborn with features suggesting congenital infection
• Outbreak investigation

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