"Negative" IgG test - why does it show trace levels of antibody?

Ok.

Last December a sexual partner and I had a genital herpes (HSV-2) scare. Neither of us had ever had an outbreak, but about a month after the first time we slept together without a condom (I know, it was a huge mistake), he broke out with something that looked exactly like herpes to his doctor. So although I'd never had an outbreak we both got tested.

I'm still not exactly sure what his sexual history was prior to sleeping with me - he said he hadn't had unprotected sex in the past couple months before me, but I believe herpes can still be transmitted from skin-to-skin contact of the areas around the genitals that condoms don't cover. He also said that it could have been through receiving oral sex from someone else.

He's been a bit evasive about it overall, so I figured testing would give better answers than guesswork with our histories.

The last time I had sex was in early July '10 (not the same man), and then nothing for around four months until sleeping with this guy in November '10.

When we both got tested in December, my results came back negative from Quest Diagnostics. I don't think I was told the actual numerical results, but IgG was negative. IgM was initially positive, but negative when put through a second, more sensitive test, so they said I was quite definitely negative.

He also tested negative, apparently with an IgG level of about 0.2. He eventually recovered from his outbreak and hasn't had any more trouble.

I thought that was the end of it, since it seemed that one of us at least should have had enough of an incubation period for IgG tests to be accurate.

Now in May '11 he gets tested again for whatever reason, and his IgG levels are still around 0.2. I would assume that's solidly negative, but the fact that the number isn't 0.0 is making him paranoid, and all his questions have made me nervous as well.

If anyone has any information as to why the IgG test result would show any level of antibody instead of none, please let me know! I apologize if this subject has already been covered and I just couldn't find it in the search.

Thank you so much.

[gracefromHHP]

you never get a 0 as a result due to the way the test is done. his was a clear negative.  I assume those are hsv2 results?

I assume you were also both tested for hsv1 too?

the herpes igm test is a greatly flawed test and current cdc recommendations advise against it being used on adults.

grace

[marginalia]

I at least was tested for both types. I'm not sure about him, but I'll double check. I actually requested not to have the IgM but it was part of some package deal that was apparently cheaper than picking individual tests. Who knows, it was still expensive but I couldn't get an appointment with my gynecologist for several weeks and I couldn't stand the wait. At least I knew not to trust that particular result :)

Thank you so much for your response - I've been getting irritated with myself and with him for nitpicking when there was clearly no reason for doubt. This set my mind at rest.

[irwinr]

"you never get a 0 as a result due to the way the test is done."

This seems very vague.  *Why* can you never get a 0.0 result?