I'm confused about what IgM testing is for. Are IgM antibodies present during and after an outbreak for a limited time or are they present after you are initially infected for a limited time? Why do people discount IgM results? If an IgM was positive, does that mean the person definitely has herpes or might have it or is it just totally useless?
Help-Concerned You're right, this has all been addressed several times. However, it's in many places and might be hard to dig out. So I appreciate the opportunity to put it all in one place.
In theory, the body produces immunoglobulin M (IgM) antibodies first, to a variety of infections, and immunoglobuin G (IgG) antibodies later. Over time, IgM antibodies tend to stop being produced entirely. Therefore, a test for IgM antibody to any particular infection may be positive before a test that detects IgG antibody. And in a person infected a long time previously, IgM antibody is absent but IgG persists.
That's the theory. In general, it holds up pretty well in young children, but sometimes not so well in adults. In adults with new HSV infection, IgM antibody against the virus doesn't actually get produced all that much faster than IgG antibody. And many people with longstanding HSV-1 or HSV-2 infection continue to produce IgM, especially when they have a new symptomatic outbreak. Thus, for HSV, IgM doesn't necessarily mean a new infection; and absence of IgM doesn't necessarily mean a longstanding infection.
On top of that, there are 2 other main problems with IgM testing for HSV. First, false positive tests are common--that is, apparent IgM antibody that simply isn't present at all, despite what the test says. This is NOT generally due to cross reaction with related viruses, i.e. HSV-1, varicella (herpes) zoster, and the like. It has to do mostly with the physical chemistry of the test.
Second, there are no type-specific IgM tests on the market--nary a one. Any true-positive IgM test for HSV is detecting antibody to HSV-1, HSV-2, or both, and can never distinguish between them.
Why do labs continue to offer such a lousy test? Several reasons there too, some reasonable, some not. Some providers still request the test; they were taught the theory, they assume it applies accurate to HSV, and don't understand the limitations of the test. (The pediatricians generally are right; IgM testing for HSV in fact remains useful in diagnosing neonatal herpes in newborns. Their immature immune systems don't crank out IgG so rapidly.) Also, some labs just keep offering the test out of habit, in the belief the providers want the test; while at the same time, the docs just assume that if the lab does the test, it must be worthwhile. (That is, a communication issue.) Also, there is simple profit motive for labs: IgM testing is very cheap but gets good pay-off from insurance companies, so the profit margin is high.
Bottom lines: Sometimes a new HSV infection in an adult indeed will be positive by IgM before IgG. But this is pretty infrequent, and it outweighed by the downsides: high risk of false positive result; and even when truly positive, there is no distinction between HSV-1 and HSV-2, which is pretty important to most patients and providers.
In response to your question, I re-contacted the people I know at Quest Laboratories. As of last month, as a matter of policy, Quest no longer does IgM testing for HSV in adults unless the provider specifically requests it. (Some individual labs might not have gotten the word yet, so some IgM testing might be done for a while.) Quest will continue to to IgM testing routinely for HSV antibody requests in newborn.
And do the bottom line for your particular situation: Totally ignore your recent IgM result with an equivocal outcome. Almost certainly it is meaningless. If you remain concerned, have an IgG test (and only IgG) 3 months after your last possible exposure.
I hope this helps. I have a feeling I will be referring future questioners to this thread quite frequently.
Grace, what do you make of my situation?? I'm in a similar situation where igg were neg and igm wsa postive- details below....
I went to my derm for just a regular checkup and mentioned to her abt the protective oral sex encounter i had 5 mths ago. As a precaution she did the hsv 1/2 igg and igm tests on me.
Plz note that i have had hsv 1/2 IGG tests at week 5, 14, 18 and they have ALL been negative. This is the FIRST time the derm did an igm also.
the results for the tests she did(week 22) were
hsv1 igg - negative
hsv2 igg- negative
hsv1/2 igm - positive(high)
she said this might be beacuse of seroconversion. she doesnt beleive igm result can be a false positive.
a few questions:
1. igm is usually high due to recent infection( i hvnt been sexually active in 5 months). how recent is recent? i kissed a girl 1 month ago but she had no lesions that i 'm aware of nor have i had ANY outbreak at all in the past month since i kissed her or last 5 months since i had protective o. sex .
2. if i do need to get tested again, when shud i get tested? how soon does igg turn positive if igm is positive( and lets assume its a true positive)
i'm not an expert, but with those results i would lean more towards that you are negative.
if you can, look at the ratio, i think it's called that. instead of just:
hsv1-igg negative, ratio .25
hsv2-igg negative, ratio .43
you should ask to see the "ratio" of them. anything 1.10 or below- you are negative. 1.10 and a little higher is somewhat debatable and would lead you to get tested again. a 3.36 or higher you are positive. even at 1.10 you need to wait and take it again.
i read on an earlier post, that some had a 10 on the igm test, which is usually a reason to take it again as it's debatable. the same person who had a 10 with the igm test got a .2 something on their igg blood test. which means they are negative.
the igm test just show if there are new antibodies caused by an infection. i'm not sure if the igm test just for hsv. if it includes other infections, then it could high due to other/unrelated infection. i'm no expert so don't take what i say as fact. just trying to help you out from the things i've read and researched.
I have had cold sores as long as I can remember myself. I have recently had complete STD testing including a non-type specific Herpes test. I actually had a cold sore the day I had my physical. I was told by my doctor that I was positive (non type specific). I have never had any vaginal outbreaks. I obviously am positive as I've had many oral outbreaks since childhood. What should I do now? I'm at loss! On one hand I would have been shocked to have a negative test if I'm having an active oral outbreak, but on the other hand... Do I warn my partner? Should I be concerned about genital herpes even though I have never had an outbreak and the test is non-type specific? I am very scared...
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