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STDs (Expert Forum)
herpeselect false positive
Answered by
University of Washington
Seattle - WA
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This forum is limited to questions about STDs other than HIV/AIDS. For questions about HIV prevention, or if you have general questions about safe sex (e.g., condoms, how to protect yourself from HIV and STDs), please visit the HIV Prevention and Safe Sex Forum
Some of the most common types of questions concern the risk of HIV or STD after a particular sexual exposure, and about symptoms that might or might not be due to HIV. If your question is along these lines, please visit the HIV Prevention and Safe Sex Forum.
herpeselect false positive
by chuckie24, Feb 16, 2005 12:00AM
had focus elisa test done in late june. hsv1 4.96, hsv2 1.61 possible exposure was in february.
i would like your opinion on the likelihood of false positive herpeselects as compared to western blot when elisa value is very low. i have read a great deal on this specific subject. retesting is suggested with value under 3.0. what is the relationship between the cutoff value, positive predictive value and population prevalence?
also, do you have any more specific insight as to why, when the manufacturer's cutoff is 1.1, i should retest with a 1.61. i am asymptomatic for both hsv1 and hsv2.
i would like your opinion on the likelihood of false positive herpeselects as compared to western blot when elisa value is very low. i have read a great deal on this specific subject. retesting is suggested with value under 3.0. what is the relationship between the cutoff value, positive predictive value and population prevalence?
also, do you have any more specific insight as to why, when the manufacturer's cutoff is 1.1, i should retest with a 1.61. i am asymptomatic for both hsv1 and hsv2.
Doctor's Answer
by H. Hunter Handsfield, M.D., Feb 16, 2005 12:00AM
, Feb 16, 2005 12:00AM
Your question reflects some very recent research, so recent it hasn't yet been published, should appear in a journal soon. I wonder if your blood was tested at either the University of Washington or the Seattle-King County Public Health lab (?). Because the research was done in Seattle, those labs now report HerpeSelect results as you describe. A few other labs might have started to do this, however.
Here is the deal. The HerpeSelect HSV-2 test can sometimes be falsely positive. The new research shows that this may be especially common in exactly the situation you describe, when the HSV-1 signal is strong and the HSV-2 ratio is between 1 and 3. When HSV-1 is negative, a ratio for HSV-2 of 1.1 or greater is definite evidence of HSV-2 infection. When HSV-1 is positive, HSV-2 results between 1.0 and 3.0 can go either way; i.e., the HSV-2 result is indeterminate. When HSV-2 is over 3.0, it's definitely positive regardless of the HSV-1 result. Happily, this doesn't happen often.
So in your case, you definitely have had HSV-1. You may or may not have been infected with HSV-2. I don't have the data in front of me, but my recollection is that the positive predictive value of the HSV-2 result in your case is in the 50% range, i.e. a coin toss as to whether you actually are HSV-2-positive. So I recommend you be retested. When it is done, ask your provider to request further confirmation if the HSV-2 result again is indeterminate, i.e. ELISA ratio between 1 and 3. The Western blot test is the classic tie-breaker; the main problem is expense and confirmation may cost an extra $150 or so. But your health insurance likely would cover it. Another option is to also have the Biokit point-of-care HSV-2 test (this is the same assay previously marketed by Diagnology under the brand POCkit). There is some (even newer) evidence that the Biokit result is a valid tie-breaker in cases like this.
Finally, Focus Technologies--manufacturer of the test--cannot (yet) legally tell labs to change the cut-off from the official 1.0 level to a higher level, such as 3.0. When a test is approved by the FDA, the parameters are set by FDA based on data submitted by the manufacturer. Until such time as the company re-submits new data, any change in interpretation is up to the individual labs doing the test. However, Focus is well aware of the new research, and probably is attempting to replicate it. So this might change in the future.
For most readers of this message: Cases like this are uncommon. Over 95% of the time, you can rely on the standard results of the HerpeSelect test.
I hope that helps-- HHH, MD
Here is the deal. The HerpeSelect HSV-2 test can sometimes be falsely positive. The new research shows that this may be especially common in exactly the situation you describe, when the HSV-1 signal is strong and the HSV-2 ratio is between 1 and 3. When HSV-1 is negative, a ratio for HSV-2 of 1.1 or greater is definite evidence of HSV-2 infection. When HSV-1 is positive, HSV-2 results between 1.0 and 3.0 can go either way; i.e., the HSV-2 result is indeterminate. When HSV-2 is over 3.0, it's definitely positive regardless of the HSV-1 result. Happily, this doesn't happen often.
So in your case, you definitely have had HSV-1. You may or may not have been infected with HSV-2. I don't have the data in front of me, but my recollection is that the positive predictive value of the HSV-2 result in your case is in the 50% range, i.e. a coin toss as to whether you actually are HSV-2-positive. So I recommend you be retested. When it is done, ask your provider to request further confirmation if the HSV-2 result again is indeterminate, i.e. ELISA ratio between 1 and 3. The Western blot test is the classic tie-breaker; the main problem is expense and confirmation may cost an extra $150 or so. But your health insurance likely would cover it. Another option is to also have the Biokit point-of-care HSV-2 test (this is the same assay previously marketed by Diagnology under the brand POCkit). There is some (even newer) evidence that the Biokit result is a valid tie-breaker in cases like this.
Finally, Focus Technologies--manufacturer of the test--cannot (yet) legally tell labs to change the cut-off from the official 1.0 level to a higher level, such as 3.0. When a test is approved by the FDA, the parameters are set by FDA based on data submitted by the manufacturer. Until such time as the company re-submits new data, any change in interpretation is up to the individual labs doing the test. However, Focus is well aware of the new research, and probably is attempting to replicate it. So this might change in the future.
For most readers of this message: Cases like this are uncommon. Over 95% of the time, you can rely on the standard results of the HerpeSelect test.
I hope that helps-- HHH, MD
if i retest positive for hsv2, the question will be where?
obviously, if asymptomatic, i can't find out. outside of beating incredible odds to have gotten hsv2 orally considering she was on acyclovir, no outbreaks or prodrome and the general idea that "hsv2 doesn't 'like' the oral area," i'm left to imagine these other possibilities: i already had it. i got it in my eye or nose. got it from sharing moist towel or some other freak transmission.
HHH, MD