|Can it differentiate active from latent infection?
|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.
|IFA IgG test
Example: Titer 1:640
|If the titer is highly elevated relative to healthy controls, it means that the patient may have had a recent infection or has a current chronic/smoldering infection. Quest Diagnostics and ARUP Laboratories are two of the only known laboratories in the USA to perform testing by IFA methodology. Their labs have 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.
(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. Chronic infections in various tissues can persist with no evidence of IgM.
|PCR DNA test on plasma or serum
(qualitative or quantitative)
|Yes. HHV-6 is never found in plasma or serum unless there is an acute infection (or the individual has ciHHV-6). However, the absence of HHV-6 DNA in the plasma/serum does not mean that there isn’t a low-level persistent infection in the tissues (e.g. heart, thyroid, brain).
|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)
|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. Usually this level is not detectable in a commercial lab.
|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. Almost all healthy individuals have low levels of latent HHV-6B in the blood. On a sensitive nested PCR tests, at least a third of the normal population should test positive for HHV-6 latent DNA.
|This test may be useful for determining if you have HHV-6A or HHV-6B but can’t tell you if the virus is active.
Staining of tissue sections from biopsies, mounted on glass slides.
|YES. This test can tell you if the proteins expressed were from replicating virus. Only Coppe Labs and IKDT perform this service commercially.
|This technique can also determine whether HHV-6A or HHV-6B is active. Analysis usually done on formalin fixed, paraffin embedded material.
|Tissue Biopsy – qualitative
|NO. This test cannot tell you if the virus is active. ViracorIBT offers a qualitative PCR test on tissues (liver, uterine, kidney, GI tract). Code: 6506
|Depending on the lab, the virus can be typed. Specimens should be sent frozen overnight, with no liquid added.
|Tissue Biopsy – quantitative
|YES. This test can differentiate between low-level latent virus and active virus with high copy numbers.
|Viracor requires 5 mg of material. Coppe can test 1 mg of material.
|ddPCR or Digital Droplet PCR to confirm ciHHV-6 status
|This ddPCR test is done on whole blood and was introduced in 2013 by University of Washington specifically to identify ciHHV-6. It cannot identify active infection.
|Patients should request this test when physicians want to confirm suspected ciHHV6.