When do igM antibodies appear?

[Johnswords]

I know when people do igM test they are usually meaningless--but for igM anitbodies, do they appear after each outbreak, or is it after last possible exposure?

The reason I ask...

My gf tested positive for hsv 2 using an igM test--I only slept with two people before her, who have had absolutely zero sexual experiences before me. Not even a kiss. So, we think her last possible exposure was 6 months ago with her last partner. She came in to the doctor with cold sores on her lip, she tested positive for hsv 1 with an igG test, but for some reason the doctor wanted to test for hsv 2 also ( she had no symptoms)  but used igM instead of igG. Would igM even still be there if her exposure was 6 months ago? Or does igM reoccur every time there is a shedding or outbreak or whatnot...

Basically, my question is, how can she test positive for an acute infection test ( igM) if assuming her last exposure was 6 months ago?

And yes, I have been tested, my results should be here soon.

[txr890]

I've seen tests which purported to have different HSV1 & 2 IgM results; in fact, the numbers were different on them for the last one i saw.  Not the same numbers for IgM HSV1 and HSV2...two distinct results.

Either way for the OP, IgM hasn't been recommended anymore anywhere, far as I know.  Get IgG after around 23 days to 40 days.  The FOCUS seroconversion curve flattens out at .2 after around 40 days meaning that 80% of people will show positive due to infection at that time.

[HowardH]

There is no such thing as an "IgM test for HSV2". As noted above, the only available HSV IgM tests are for both types 1 and 2 and do not distinguish between them. All I can guess is that like many average practicing physicians, your partner's doctor doesn't understand the details of HSV blood tests and how to use them.

[Johnswords]

Well she did test positive for hsv 1--on top of that, she had oral cold sores, which most of the time is hsv 1 from what I have read. The whole purpose of the visit was the cold sores on her lip, so she was having an obvious outbreak for hsv 1. I just cant grasp why the doctor would do a igM test for hsv 2, if she tested positive for hsv 1, and was having a cold sore outbreak. Wouldn't it be a no brainer that she would test positive for both in that case with that test?

[HowardH]

The problems with HSV IgM testing have been described frequently -- use the search function on this and the now-defunct herpes and STD expert forums.

In theory, IgM appears before IgG antibody, then goes away -- so IgM+/IgG- means new infection (probably under 6 weeks?), both pos is intermediate, and IgM-/IgG+ means longstanding infection, probably usually 3 months or more. (The actual times have never been researched carefully, so these are only educated guesses.) The problem is that with HSV, IgM antibody often never appears; and when it does, it often persists forever, or rises again with a recurrent outbreak. Further, IgM testing doesn't distinguish between HSV1 and 2.  A positive can come from either or both viruses, with no way to know which is actually responsible for the resulty. On top of that, the IgM test often gives false positive results; a positive IgM test is never reliably positive.

By far the most likely explanation for the results in your partner, apparently positive by IgM more than 6 months after a potential exposure, is that it's a false result and she doesn't have, and never had, HSV2; or that she has HSV1, like half of all adults in the US.