1. It is impossible to tell if a patient has ciHHV-6 from either the CSF or plasma (Leong 2007) and a ciHHV-6 individual can have a negative PCR in a plasma sample. (Tanaka Taya 2004).
2. A whole blood PCR DNA test can easily differentiate ciHHV-6 from non ciHHV-6 in almost all cases (Leong 2007). If the HHV-6 viral load in whole blood is > 500,000 copies/ml, it is probably ciHHV-6 (Exceptions: acute DIHS, GVHD). Additional information on testing can be found at the CIHHV-6 Testing page.
4. CiHHV-6 replicates in response to certain chemicals such as HDAC inhibitors, in vitro (Arbuckle 2010).
5. CiHHV-6 mothers can infect their non-ciHHV-6 infants via the placenta, resulting in congenital infection (Hall 2010, Gravel 2013).
6. CiHHV-6 may be overly represented in certain patient populations such as children referred for encephalitis. The rate of ciHHV-6 was 3.3% in one UK study of pediatric encephalitis cases (Ward 2005).
7. It is impossible to track antiviral response to therapy in a ciHHV-6 patient because of the high a background of a high level of DNA from integrated HHV-6. Only mRNA testing can identify active infection in a ciHHV-6 case and this assay is not available in most laboratories.
8. Clinical judgment must be used for the decision to treat a ciHHV-6 case with symptoms of reactivated HHV-6.
9. Antiviral drugs will never reduce serum, plasma or CSF levels to zero, and must be used with caution in ciHHV-6 patients (Ward 2006).
10. Serum DNA levels are always higher than plasma DNA levels due to cell lysis in the clotting process (and DNA leakage to the plasma). If plasma samples are sent overnight instead of centrifuged immediately, however, the plasma load will be quite high due to cell lysis in transit.
TIPS: The University of Washington has a new ciHHV-6 test that is highly accurate. There are two commercial laboratories in the US that can give a 24 hour result on whole blood PCR for HHV-6 PCR DNA testing Viracor-IBT and Focus Diagnostics/Quest laboratories. However, you must contact the lab and request a whole blood PCR DNA test or they will run the test on plasma. Additional information on testing locations and availability can be found at the CIHHV-6 Testing page.