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The most practical method to determine if an individual has CIHHV-6 is to perform a whole blood quantitative PCR test. If the level is above 500,000 copies per ml in the absence of an acute reactivation, then the individual has a high likelihood of having CIHHV-6. Although the viral load of a non-CI individual can be higher than 500,000 copies per ml of whole blood on rare occasions, this typically occurs only during episodes of graft vs host disease (GVHD) or in association with extreme hypersensitivity reactions (DIHS/DRESS).
If there is uncertainty, other ways to confirm CIHHV-6 are to test the patient’s parents (at least one of the two would have a high positive result) or perform a qualitative PCR DNA test of the individual’s fingernails or hair follicles. Only CIHHV-6 individuals will have HHV-6 in the DNA of hair follicles or fingernails. In these cases, a qualitative PCR test would suffice.
Another means of confirming CIHHV-6 is to test the patient’s parents or siblings for HHV-6 by PCR. Finally, if the patient is undergoing an acute illness, or primary infection, sequential testing will reveal CIHHV-6 status because the extremely high viral loads in these situations are very brief. FISH analysis can confirm integration but is not necessary or practical in clinical practice.
USA
Several commercial laboratories offer testing for HHV-6 by quantitative PCR. In the US, Viracor (Lee’s Summit, MO), Quest/Focus Diagnostics (Cypress, CA) and ARUP (Salt Lake City, UT) offer whole blood quantitative PCR DNA tests for HHV-6. Viracor does have a special CIHHV-6 test that includes a white blood cell count so that the number of DNA copies per WBC can be calculated. Variant typing is also available at these labs. Labcorp (Burlington, NC) does not offer quantitative PCR testing on whole blood, but will analyze a whole blood sample for ciHHV-6 by special request.
Please note that it is important that the request be made explicitly for a whole blood test as the default specimen is plasma, and a PCR DNA test on plasma is not useful for identifying CIHHV-6.
Europe
In France, quantitative PCR DNA testing on whole blood is available in most university hospital virology laboratories. In Germany and for Europe, IKDT (Institut Kardiale Diagnostik und Therapie, Berlin) and R.E.D. Laboratories in Belgium offer quantitative PCR testing for HHV-6 DNA. This is an incomplete list. If you are aware of other laboratories in the UK or Europe, please email us at information@HHV-6Foundation.org.
