IgG blood tests are good but not perfect.
With the most common test (HerpeSelect®), strong positive (HSV2 index 3.5 or more) is proof of infection, regardless of symptoms. Negative (under 0.9) also is conclusive. Index >1.1 is officially positive, but many results 1.1-3.5 are false. Other IgG tests less well studied. Such uncertainties are why HSV blood tests often are controversial.