Herpes Blood Test (HSV IgG) — Should You Get One?
Content last reviewed 2026-09-12 · Educational information — not medical advice
Quick answer
Type-specific HSV-1/HSV-2 IgG blood tests detect antibodies 4–12 weeks after exposure. They can't tell you WHERE outbreaks will occur or guarantee symptom behavior — which is why guidelines advise against universal screening but support targeted testing with counseling.
How does herpes testing work?
Blood tests measure type-specific IgG antibodies distinguishing HSV-1 (oral-predominant, increasingly genital too) from HSV-2 (genital-predominant). Active sores swabbed directly via PCR give the definitive diagnosis during outbreaks; blood work answers the between-outbreaks question.
Why don't doctors just screen everyone?
CDC advises against universal HSV screening deliberately: without accompanying counseling, positives create anxiety disproportionate to clinical severity for many people, IgM tests are unreliable garbage, and even good IgGs miss early infection. Targeted testing — symptoms, partner diagnosis, or genuine peace-of-mind need — makes sense; reflex screening often doesn't.
Interpreting index values
IgG reports an index: <0.9 negative, 0.9–1.1 equivocal (repeat in 2–4 weeks), >1.1 positive. Low-positive values (1.1–3.5) occasionally represent false positives — confirmatory inhibition assays or repeat testing resolves ambiguity before life decisions get made over a borderline number.
If positive — then what?
Genital herpes becomes a manageable skin condition: antivirals cut outbreak duration and asymptomatic shedding dramatically (daily suppression reduces transmission risk substantially). Disclosure conversations matter ethically and legally in some states. The diagnosis changes logistics, not life trajectory, for the vast majority of people.
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Frequently asked questions
Can I test during my first outbreak?
Swab PCR during active sores is the gold standard — blood antibodies haven't developed yet (negative IgG early on is expected).
Do cold sores mean HSV-2 protection?
HSV-1 infection partially protects against HSV-2 acquisition; oral HSV-1 can infect genitals through oral sex regardless.