The most practical method to determine if an individual has chromosomally integrated HHV-6 (ciHHV-6) is to perform a whole blood quantitative PCR DNA test for HHV-6. If the level is above 500,000 copies per ml in the absence of an acute illness, then that individual has ciHHV-6. The viral load of a non-ciHHV-6 individual can occasionally be higher than 500,000 copies per ml of whole blood, but only when the patient is extremely ill – during encephalitis or an acute episode of graft-versus-host disease (GVHD) or extreme drug hypersensitivity (DIHS/DRESS). Test results suspicious for ciHHV-6 can be confirmed by testing the patient’s parents (at least one of the two would have a high positive result).
There are other means of confirming ciHHV-6 status, but a whole blood PCR will suffice in most situations. FISH analysis can confirm integration. Also, the fingernails or hair follicles of ciHHV-6 individuals can be tested by qualitative PCR. Only ciHHV-6 individuals would have a positive PCR test on a fingernail or hair follicle.
USA
University of Washington
The University of Washington’s Department of Laboratory Medicine has now developed a whole blood qPCR for HHV-6 that aids in the diagnosis of ciHHV-6. The group is running this test in parallel with a newly developed rapid and accurate droplet digital PCR (ddPCR) assay for diagnosis of patients with ciHHV-6. Most quantitative PCR assays are not precise enough to give an accurate ratio of HHV-6 DNA copies per cell. The ddPCR can provide a ratio of HHV-6 DNA copies per cell with great precision, and will be the first clinical test in the USA able to determine definitively if a patient has ciHHV-6. Download the requisition form HERE.
Coppe Labs
In addition, three important tests for HHV-6 are available through Coppe Labs, including two assays that are not available commercially at any other location in the US: the mRNA test for assessing active infection and immunohistochemistry analysis for biopsy samples. The company utilizes the reverse transcription polymerase chain reaction (RT-PCR) technique as opposed to traditional DNA PCR, in an effort to more accurately document active replication of the virus (Pradeau 2006). Although plasma HHV-6 DNA load correlates with active infection , only a test of mRNA can differentiate between active and latent infection in a patient with ciHHV-6. Therefore, transplant physicians must currently use clinical judgment rather than viral load analysis in making a decision to treat a symptomatic patient with ciHHV-6. This test should prove to be invaluable for transplant physicians, since failure to treat can result in HHV-6 encephalitis or other serious manifestations, but antivirals can cause serious side effects such as bone marrow suppression or kidney toxicity. Coppe Lab’s HHV-6 immunohistochemical (IHC) staining will help detect the presence of HHV-6 proteins in a variety of fixed and paraffin embedded tissues, thereby confirming not only that the virus is present, but also which cells contain the virus and whether the infection is active or latent. In addition, the IHC test will be able to determine if the infection is caused by HHV-6A and HHV-6B.
Coppe Labs will also offer a hair follicle test to determine ciHHV6 status. It is not possible to differentiate ciHHV-6 patients from those with active infection using a plasma PCR DNA test. However, a simple whole blood PCR DNA test can identify a ciHHV-6 patient in all situations except an acutely ill patient with encephalitis, GVHD or DRESS/DIHS (conditions associated with extremely high HHV-6 DNA loads). ciHHV-6 patients typically have whole blood DNA loads of over 2 million copies/ml or several logs higher than the expected viral load in a transplant patient with reactivation. In those situations, the Coppe hair follicle test could definitively identify a ciHHV-6 patient. To learn which HHV-6 tests are offered by Coppe Labs or visit their website.
Others
Several larger commercial laboratories also offer conventional testing for HHV-6 by quantitative PCR. In the USA, 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. 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 info@hhv-6foundation.org.
For more information on ciHHV-6, visit the Foundation’s “What is ciHHV-6?” page, as well as here to download a comprehensive ciHHV-6 Q&A published by dozens of international experts in the top journal Reviews in Medical Virology.