Is a penis swab on the inside accurate to detect herpes?
For men who have active herpes lesions or blisters, the gold standard is a viral culture test or nucleic acid amplification test (NAAT) of a sample of skin, crust, or fluid from the blister/lesion, which is usually obtained with a gentle swab of the area.
Whilst no tests are 100% accurate, a NAAT should only come back positive if you have the virus present in the lesion. The results of the NAAT test are highly reliable. The diagnosis of genital herpes can often be clinical and not require a swab at all.
However it's easier to diagnose genital herpes at the beginning of an outbreak when it's possible to see the blisters and take a sample of fluid from a blister or sore before it starts to heal. This is because an accurate diagnosis will depend on the amount of virus that is being shed at the time, the stage of the blisters or sores and the type of test that is used on the swab specimen. The doctor or nurse will talk to you about how accurate your test result might be.
Sources:verywellhealth.com - How viral cultures detect viruses during STD testing