HSV 1 IgM

Function

The HSV 1 IgM test is a serological assay used to detect Immunoglobulin M antibodies against Herpes Simplex Virus Type 1. IgM is generally the first antibody produced by the immune system in response to a new infection. HSV-1 is traditionally associated with orofacial lesions (cold sores), though it is increasingly a cause of genital herpes.

Why it is Ordered

This test is typically ordered when a patient presents with active sores or blisters to determine if they are experiencing an acute, primary infection. It is also used in neonatal settings where a mother has active lesions, or in cases of suspected viral encephalitis.

Associated Conditions

• Primary HSV-1 Infection: Indicated by high IgM levels with negative IgG.
• Reactivation: While IgM is associated with new infections, it can reappear during the reactivation of a latent virus in some individuals.
• Cross-Reactivity: It is important to note that IgM tests can sometimes cross-react with HSV-2 or other herpesviruses like Varicella-Zoster (VZV).

Clinical Limitations

IgM testing for HSV is often discouraged by many health organizations (like the CDC) in favor of PCR or type-specific IgG testing. This is because IgM cannot reliably distinguish between a first-time infection and a flare-up, and it may stay elevated for months, leading to confusion regarding the timing of the infection.