Does positive HSV IgG with negative IgM indicate prior infection?

HSV serology is commonly misinterpreted as a marker of current illness. In this setting, the clinically meaningful result is a confirmed type-specific IgG result; IgM adds little reliable information about infection timing or severity.

Serologic interpretation

• A positive type-specific HSV IgG generally supports prior HSV infection and durable humoral immune memory. IgG typically develops in the weeks after infection and persists long term, often indefinitely.
• Negative HSV IgM does not reliably date infection or exclude a recent acquisition. IgM is not type-specific, may be absent in primary infection, and may occur during recurrent HSV episodes; it is therefore not recommended for routine diagnostic interpretation.
• A confirmed IgG-positive/IgM-negative pattern is most consistent with established infection, but cannot determine when transmission occurred or distinguish remote from relatively recent infection.

Assay considerations

• HSV-2 IgG results at low positive index values—particularly <3.0 on enzyme immunoassays—can be false positive. Confirmation with Biokit or Western blot is appropriate before assigning an HSV-2 diagnosis in this range.
• An early negative IgG result can occur before seroconversion and does not exclude infection if exposure was recent.

Acute/systemic disease evaluation

• HSV antibody testing cannot establish disseminated HSV infection, HSV hepatitis, or HSV encephalitis. These syndromes require testing from the relevant clinical compartment.
• Active mucocutaneous lesions should be assessed by lesion NAAT/PCR. Suspected disseminated disease or HSV hepatitis warrants plasma/serum HSV PCR, often alongside tissue testing when clinically appropriate. Suspected encephalitis requires CSF HSV PCR; if initial testing is negative but suspicion remains high, repeat CSF testing in 3–7 days is recommended.
• In severe compatible hepatitis or liver failure, empiric IV acyclovir may be warranted while direct testing is pending.

Bottom line

• A valid positive HSV IgG with negative IgM generally indicates prior infection and immune memory, not proof of an acute systemic HSV process; diagnosis of acute disease depends on syndrome-directed PCR testing.