If you’re an investigator or physician interested in diagnostic approaches for the detection of HHV-6 in the laboratory, please visit our page focused on HHV-6 Testing for Researchers
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TEST |
Can it differentiate active from latent infection? |
Comments |
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ELISA IgG test Example: “positive >1.0″ |
No. These results are intended to give only “yes/no” answers to whether you are exposed to the virus in the past. | An ELISA> 5 in an adult MIGHT be a clue of an active infection, but only the antibody tests done by IFA can tell you with precision how elevated the antibodies are. |
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IFA IgG test Example: Titer 1:640 |
Sometimes! If the titer is highly elevated, it means that the patient has had a recent infection or currently has a chronic infection. Titers vary by laboratory. Focus Diagnostics (Quest) has a median antibody titer between 1:80 and 1:160 for controls. Other labs have much lower control titers. | If the patient has an immune deficiency with low total IgG, then the antibody titer will not be elevated. If HHV-6 is the only antibody titer out of five viruses to be elevated above average, then this indicates possible HHV-6 infection. |
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IgM test (ELISA or IFA) |
Yes. IgM only appears during an active infection or for 2-3 months after an active infection. | The absence of an IgM antibody does not mean you do not have a active infection. Low level infections can perist with no evidence of IgM. |
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PCR DNA test on plasma or serum (qualitative or quantitative) |
Yes. HHV-6 is never found in plasma or serum unless there is an active infection. However, the absence of HHV-6 DNA in the plasma/serum does not mean that there is no active infection. HHV-6 does not circulate in the plasma/serum except during the initial infection and transiently during an acute infection. | Any positive test result should be repeated with a quantitative test. Also, a whole blood test should be ordered to rule out chromosomally integrated HHV-6 which occurs in 1% of the population. (See CIHHV-6) Someone who inherits HHV-6 in the chromosome will always be positive in the serum, whether the HHV-6 is active or not. |
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Quantitative PCR DNA test on whole blood Example: 1200 copies/ml |
Yes. If the viral load is >200 copies per ml or 20 copies per microgram of DNA then this is an active infection. | Healthy persons will have very low viral loads, typically less than 20 copies/ml in the whole blood. |
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Qualitative PCR DNA test on whole blood Example: “Positive” with no numerical value given |
No. This test is useless for differentiating active from latent infection, and should be avoided. Most healthy individuals have small levels of latent HHV-6B in the blood. | This test can be useful for determining if you have HHV-6A or HHV-6B Finding HHV-6A DNA is unusual and follow up testing might be worthwhile. |
While both LabCorp and Quest laboratories offer a basic qualitative ELISA test for HHV-6, additional testing is necessary to determine a proper diagnosis of HHV-6 infection for the reasons listed above. FOCUS Diagnostics, a division of Quest Laboratories, offers many of the above tests that may help to properly identify an HHV-6 infection. Patients may have blood drawn at any Quest laboratory, and request that these specific testing inquiries be forwarded to FOCUS Diagnostics to ensure proper results.
