In 2012, the International Committee on Taxonomy of Viruses classified HHV-6A and HHV-6B as separate viruses (prior to that they were considered subtypes of HHV-6). Ref: 1 However, even though HHV-6A is a distinct and separate virus, since nearly all HHV-6 tests cannot distinguish between HHV-6A and HHV-6B, and since HHV-6 is found in nearly everybody (so nearly all HHV-6 tests are going to come back positive for having the virus), by standard labs tests, it is hard to know whether you might have HHV-6A or not. According to the HHV-6 Foundation, testing laboratories that can detect HHV-6A include: • Viracor-IBT Laboratories — HHV-6 Quantitative Real-time PCR • Focus Diagnostics • Wisconsin Viral Research, who have now become Coppe Labs. HHV-6A seems to be a significant virus for ME/CFS: One study of 36 ME/CFS patients and 24 healthy controls found HHV-6A in the peripheral blood mononuclear cells (PBMC) of 22% of ME/CFS patients, but only in 4% of healthy controls. This study of 13 ME/CFS patients and 13 healthy controls found HHV-6A in the PBMCs of 31% of patients, HHV-6B in the PBMCs of 23% of patients, and no HHV-6A nor HHV-6B found in the PBMCs of healthy controls. However, although the above studies found little to no HHV-6A or HHV-6B in the PBMCs of healthy controls, somewhat confusingly, this study of healthy individuals found HHV-6A in 16% of subjects' PBMCs, and HHV-6B in 98% of subjects' PBMCs.