Herpes Simplex Virus IgM in Dehradun

What is a Herpes Simplex Virus IgM?

IgM is generally the antibody of first response, and for many infections its presence indicates a recent or current episode. For herpes simplex that logic breaks down more than for most viruses, and this needs saying plainly because HSV IgM is one of the more frequently misinterpreted tests in practice. IgM can be positive in a first infection, but it can also appear during a reactivation of a long-standing infection, so it does not reliably distinguish new from old. It can persist for months. It cross-reacts, including with varicella zoster, the chickenpox and shingles virus. And it can be negative in a genuine first infection tested too early. The consequence is that a positive HSV IgM cannot be used to conclude that someone has just acquired herpes, and in a relationship context that misinterpretation causes real harm. Where the clinical question is whether an active lesion is herpes, a PCR swab taken directly from the sore is far superior: it is direct, type-specific and definitive, and it should be the first choice whenever a lesion is present.

Why take this test?

HSV IgM is advised in limited circumstances, generally by a specialist, and usually together with IgG so that the pair can be interpreted as a whole. It may be used where a first infection is suspected in a pregnant woman, particularly late in pregnancy, since that scenario carries the greatest risk to the newborn, and where a neonate is suspected of having a herpes infection, which is a medical emergency requiring immediate paediatric care. It is sometimes used in suspected disseminated infection in an immunocompromised patient. It is not a good test for the common question of whether a genital sore is herpes: swab the lesion instead. Take any positive result to your doctor rather than drawing conclusions, particularly about when or from whom an infection was acquired, because this test genuinely cannot answer that and attempts to make it do so cause avoidable damage.

• Suspected first herpes infection in pregnancy, with IgG
• Suspected neonatal herpes, which is a paediatric emergency
• Suspected disseminated infection in an immunocompromised patient
• Where no lesion is available to swab and IgG alone is inconclusive
• Not the right test for an active sore — swab the lesion instead
• Not usable to establish when or from whom infection was acquired

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