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False positive herpes test
Written and reviewed by Slava Fuzayloff | Published on September 16, 2024
What does the “false positive” test mean?
It is when the test shows a person has a specific disease, but this is not true.
What is the chance of a false positive herpes test?
Here, we will discuss the IgG herpes test, also known as the “herpes select test.”
Any test has a false positive value, but the one for herpes is unusually high. This means that the current herpes IgG test is not exact.
According to the US Preventative Task Force, up to 50% of herpes select tests are false positives [1] Genital Herpes Infection: Serologic Screening https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/genital-herpes-serologic-screening , so no routine test is recommended [3] Screening for Genital Herpes https://www.cdc.gov/herpes/testing/index.html .
What is more interesting is that the research false positive rate for the IgG test is different for different Herpes types:
✓ For HSV-1, the positive IgG test is more reliable, and the Washington University (WU) western blot test confirmed more than 80% of the cases.
✓ For HSV-2, only 50.7% of positive IgG tests were confirmed by the WU western blood test.
What can cause a false positive herpes test?
My comments here are regarding the only commercially available herpes blood test - the IgG herpes test.
There are a few reasons for false positive herpes testing:
✓ Cross-reactivity (when antibodies can react with similar-looking molecules) with similar viruses such as Varicella zoster virus (VZV), CMV (cytomegalovirus), and other things such as flu or even getting the vaccine.
✓ Improper storage and handling of the blood sample
✓ Lab error
Is it true that a low-index HSV positive test is most likely a false positive?
The short answer is that it depends on the herpes type.
So, what is a low positive index?
An index of more than 1.1 is considered positive by the herpes select IgG Ab test.
However, some experts consider an index below 3.5 on the test a “low positive” and likely a false positive.
However, researchers from Washington University (the only place where the confirmatory HSV Western blot tests can be done) show that this might be true for HSV-2 but not valid for HSV-1:
✓ Most HSV-2 positive low index test results on the commercially available “herpes select test,” or IgG Ab, frequently tested negative with the more sensitive Western Blot test.
✓ The reverse is true for HSV-1—more people tested positive with a more sensitive Western Blot test than a regular IgG Ab test.
The other test, called Herpes Simplex Virus Type 2 (HSV-2) IgG Inhibition Assay that Quest manufactured [2] Herpes Simplex Virus Type 2 (HSV-2) IgG Inhibition Assay https://www.questdiagnostics.com/healthcare-professionals/clinical-education-center/faq/faq73 , confirms that 50% of the initial low positive (<3.5) test shows as negative with the inhibition test.
Can a yeast infection cause a false positive herpes test?
No, yeast infection in females cannot cause a false positive Herpes IgG test.
Yeast infection affects the same area as herpes; some symptoms can be similar.
Can HPV cause a false positive herpes test?
The positive HPV test cannot alter or affect the Herpes Select IgG test.
Herpes or HSV and HPV belong to different virus types, and it is not known to affect the herpes IgG test.
Source
-
Genital Herpes Infection: Serologic Screening
https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/genital-herpes-serologic-screening -
Herpes Simplex Virus Type 2 (HSV-2) IgG Inhibition Assay
https://www.questdiagnostics.com/healthcare-professionals/clinical-education-center/faq/faq73 -
Screening for Genital Herpes
https://www.cdc.gov/herpes/testing/index.html
