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Confusiion over other IgM Herpes posts
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Confusiion over other IgM Herpes posts

Sorry to drag up a frequent topic but I'm confused by the many threads on IgM tests being worthless.   I had thought this was because so many have HSV1 and the test is not type specific.  Also because a lack of the IgM antibodies doesn't mean you don't have Herpes.  

However in one thread you responded that you can't be positive for IgM and not have either strain.  So does this mean that when you say the test has a high incident of false positives that its because many have HSV1?  Or because the test is often falsely positive for some other reason? If its not due to some other reason then I'm confused by the posts where people said their Herpeselect test were negative but IgM was positive and they were told they should disregard the IgM results.


In my case, I tested negative with Herpeselect a year or two ago and had been in a committed relationship for years.   After a recent new encounter I was tested again ater 18 days with Herpselect (I know that is too soon for a new possible exposure).  Still, it was negative for both types enforcing my earlier position that I didn't previously have either strain.   However, an IgM test at 21 days was equivocal (1.01) so now I don't know what to make of it.

Tags: negative, test
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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.

HHH, MD
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Thanks! Its an important topic especially since its really hard to find any consistant information searching the web.   I found hardly any other sites talking about false positives with the IgM test but many saying the reason not to use the IgM test was because of false negatives and not being type specific.  As you point out these can be two valid reasons.  However, without knowing that there is also a high incidence of false positives,
individuals can easily assume that if they didn't previously have any strain of HSV that a positive IgM test was a sure bet they had just contracted one of them.   This misunderstanding is compounded by a lot of print saying false positives for Herpes almost never occur without specifying which "test" that statement was referring to.  While a bit hard to find, you can see from this forum that there are actually quite a few incidents of false positives for people who do not have HSV with the IgM test and from your comments it sounds like even a lot more clinical data supports this as well that isn't so readily available to the public.

I believe another point to make is that equivocal test results means you can't tell either way.  I think many assume (or worry) that this indicates they tested just a bit too early or too late and that the result will surely become positive as time goes by.  Perhaps, but correct me if I'm wrong, if there was any statistical data supporting this notion to any degree I wouldn't think the result would be equivocal by definition.  It doesn't help that I found a lot of contradicting information as to when the IgM test would be most reliable in the first place.  Some said any time less than four weeks, another said 2-3 weeks dropping off sharply after that, and one provider of this test said 3-5 weeks.  Being at three weeks for my test, I know that was my first thought since I was on the early side according to one reference and on the late side according to another.  

Finally thanks for emphasizing that cross reaction is not generally a cause for false positives.  For the information I did find through Google on IgM false postivies, this was pretty much the only explanation.  Thus again easily causing people to worry that they either had one of these other conditions or that they truly did have HSV because they knew they didn't.

Since I misspelled confusion with a double 'i' it should be easy to reference through a search. <smile>

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The doctor NEVER stated that you CAN'T have a positive IgM test and not have either strain of HSV.  He has stated the opposite many times.  I believe the thread that you a referring to is the thread titled, "Not sure what to make of results" posted on 1/29/06(if you do a search site for "herpes igm" it is on the second page of the results).  In this thread their was a misunderstanding, the doctor was responding to the comment under the question.  This issue was cleared up 2 days later in the thread titled "Confusion" on 1/31/06(directly above the "Not sure what to make of results" thread when "herpes igm" is searched for).  The doctor says " Your interpretation is correct. You can have a positive IgM test and not be infected with either HSV-1 or HSV-2."  He also goes into a very well put explanation on this thread why IgM test for all viruses give false positive results.

As you probally are well aware of by now, their are numerous threads where people have positive IgM test but negative for both HSV-1 and HSV-2 on the IgG test.  That is why IgM test are described as "worthless".  Whether negative, equivocal or positive the test should be totally disregarded.  It is possible for some with one or both strains of the virus to have a negative IgM and someone with niether HSV-1 or HSV-2 to have a positive IgM.

As far as the non specific IgG test, they are reliable only when negative.  As you know, the older non specific IgG test detect antibodies for both HSV-1 and HSV-2 but can not tell you which strain you have.  It can only tell you if you have HSV antibodies in your blood.  If positive, it means you either have HSV-1, HSV-2 or both.  Since most people want to know what strain it is they have, these test are not reccommended.  Their are atleast 7 different type of antibodies your body will produce for HSV. The type specific Herpesselect test look for 1 antibody protein, that is "glycoprotein G"(gG-1 for HSV-1, gG-2 for HSV-2).  This is the antibody the actually "surronds" or "envelopes" the outside of the HSV virus. The Herpeselect test can differentiate between HSV-1 or HSV-2 when this antibody protein is tested for.  Thats why it is type specific.  I hope this makes sense.
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If you don't find the answers you are looking for by searching the previous posts you can post a new question using this link http://www.medhelp.org/forums/STD/entre.htm.

Regarding my previous response, I wasn't saying a non-specific test is not a concern.  What I was saying is he has one test that says he has either HSV1 or HSV2 and another test saying he has neither.  Both can't be right.   I then was saying the Type specific HerpeSelect test is the best test to use for general testing.  So if I had to pick the results of one or the other I would go with the HerpesSelect results.  Non-type specific tests typically are older technology and more prone to false results.

As for who gave it to who, you probably will never know unless after five or so months since your positive test he is still negative.  In which case, you almost certainly did not get it from him.  He still may have it as it can take up to three months but rarely up to five or so months from your last sexual encounter together to test positive even with the HerpeSelect.  To make this a little easier to understand, let's say you both contracted it on the same day.  He might test positive in four weeks or less while it might take you three months.  So you just don't know who had it first unless there was enough time (3-5 months) between one of you testing positive and the other negative.

As I said earlier, don't feel bad about yourself.   There are people from all walks of life that have Gential (genital) Herpes...rich, poor, famous, beautiful, smart, etc...   The disease does not define you as a person.  Statistically some of your friends have the disease as well and obviously someone you knew if not your ex gave it to you as well.  No one wants to hear they have Herpes but really the psychological burden is much worse than the disease itself.   If your friends can't be supportive then they're not real friends.  Then again unless you're sleeping with them there's no reason to tell them either.  Just don't keep it all bottled up inside.  Find a support group or someone you can confide in; friend or otherwise.   As a related note, a good friend of mine told me she was HSV2 positive years ago, long before I knew anything about the disease and we're still good friends and she's a wonderful person.

I wish you all the best.

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