Cytomegalovirus IgM (CMV) in Dehradun

What is a Cytomegalovirus IgM (CMV)?

CMV IgM is the first-response antibody and appears with a new infection, but as with other herpes-family viruses it is a considerably less clean signal than its equivalent for many other infections. It can also rise during reactivation of a long-standing latent infection, it can persist for many months after a primary infection, and it cross-reacts with other viruses, particularly Epstein-Barr virus. The consequence is that a positive CMV IgM cannot by itself establish that someone has just been infected, which is precisely the question that matters most in pregnancy. Resolving it usually requires an IgG avidity test, which measures how tightly the IgG antibodies bind: antibodies mature over months, so high avidity indicates an older infection, likely predating the pregnancy and therefore of much lower risk to the baby, while low avidity suggests a recent one. Paired samples showing a rising IgG can also help. Because congenital CMV is a leading infectious cause of hearing loss and developmental problems, this sequence of confirmation matters, and it belongs with an obstetrician rather than being read from a report.

Why take this test?

CMV IgM is advised in pregnancy where there has been a flu-like or glandular-fever-like illness with fever, sore throat, swollen lymph nodes and fatigue, where an ultrasound finding raises the possibility of congenital infection, or where documented exposure has occurred. It is used together with IgG so that the pair can be interpreted, and a positive result generally leads on to avidity testing rather than to any conclusion. It is also used in immunocompromised patients, including transplant recipients and people with advanced HIV, where CMV disease can affect the eyes, gut and lungs, though in that group viral load testing by PCR is usually more informative than antibodies. It is not a routine antenatal screening test in most protocols, precisely because the false-positive and persistence problems generate alarm out of proportion to the information gained.

• A flu-like or glandular-fever-like illness during pregnancy
• An ultrasound finding suggesting possible congenital infection
• Documented CMV exposure in pregnancy
• Suspected CMV disease in an immunocompromised patient
• Always alongside IgG, and usually followed by avidity testing
• Not a routine blanket antenatal screen in most protocols

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