[Question #2099] Quest IgM IFA test

47 months ago
My question is about the usefulness of the current version of Quest HSV 1/2 AB (IgM), IFA W/RFL to Titer   (IFA = ImmunoFluorescence Assay)

Hx:    Eleven weeks ago I spent 5 days with an HSV 2 positive woman.   She has been positive for 20 years, was asymptomatic and taking acyclovir but we did not use condoms for vaginal.   I have not experienced any symptoms.    However, since the CDC says this situation is a valid one for testing I requested testing at 9 weeks post contact when I went back to the States for a routine physical.   I live in MX but she lives in the US.      I was expecting the MD to order an IgG test for HSV 2 (albeit a little early) but instead what I got was the IgM specified above but the lab report explicitly states that it was for HSV 2 IgM and used the IFA method.     The result was
HSV 1 IgM negative;   HSV 2 IgM positive, titer 1:20;

I understand that everyone lambasts the IgM because it is not type-specific and is known for false-positives but I want to know if this method is the same or similar to the method from 20 years ago (Example:
Am J Clin Pathol. 1986 Dec;86(6):765-8) or if this is new and improved.    I'd never seen an IgM test claim to be type-specific.

Regardless, next week I plan to get an IgG here (at 12 weeks post) although I have yet to get a list of the tests available here.   I'd prefer a Western Blot if I could but I don't think that is possible from here; maybe you can tell me if that can be done.  

I'd like your comment and recommendation on this.   Thanks.
Terri Warren, RN, Nurse Practitioner
Terri Warren, RN, Nurse Practitioner
47 months ago
I've tried and tried to find out more information on the IgM test through Quest without success.  As far as I know (and from what I've seen very recently), the IgM test still has problems with false positive - in my experience, a positive is wrong at least 70-80% of the time - that is, the person who has a positive IgM never goes on to serconvert.  The IgM can also be positive with recurrent disease so I don't know how to interpret this result, given that you don't have an IgG test to compare it to.  As for comparing it to a test that was discussed 20 years ago, I'm sure it has been updated since then, I just don't think, given what I've seen recently in my own patients, that it is good enough for prime time. 
We can arrange a western blot from Mexico - I can help you with that should you decide that's what you would like to do.  We've done test for people in Sweden, China and London - I'm sure we can do it for you if that's what you want to do.

Terri
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47 months ago
Thanks Terri

Hopefully we can leave this case open for a while and I will get the IgG next week and I'll report back.    With that in hand we should have a clearer picture to help decide how to proceed.    Thanks.
Terri Warren, RN, Nurse Practitioner
Terri Warren, RN, Nurse Practitioner
47 months ago
We will definitely keep this open, yes.  I would also remind you that if you've never been tested before for HSV 2 and you're positive now, it won't be possible to know when you became infected.  Just throwing that out there!

Terri
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46 months ago
I had the HSV 2 IgG done at 13 weeks and it was .5, seemingly safely in the negative range (<.9 = Neg) .  This lab in MX uses the quimioluminescencia method which translates to chemiluminescence.    As I read about this method it is clear that this technique is
very different from the immunoflorescence technique.  

From Wikipedia:

Chemiluminescence differs from fluorescence or phosphorescence in that the electronic excited state is the product of a chemical
reaction rather than of the absorption of a photon. It is the antithesis of a photochemical reaction, in which light is used to drive an
endothermic chemical reaction.   Here, light is generated from a chemically exothermic reaction.

Regardless, it still begs the question about the reliability of this test method (the thing that really counts!).  Do you have data on
the reliability of this method?   

Thanks.


Terri Warren, RN, Nurse Practitioner
Terri Warren, RN, Nurse Practitioner
46 months ago
I don't have data specifically about this test, sorry, but if it is in their negative range, you are likely OK. That's a good thing. 
Thanks for updating me on your IgG result, as I requested.

Terri
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