IgG and IgM antibodies against HHV-6 were measured from the panel of 26 serum specimens, collected once before HSCT, from the patients with different hematological disorders using a commercial enzyme immunoassay (PanBio). The results obtained with both HHV-6-specific IgG and IgM tests were expressed in PanBio units (PBU). The PBU is calculated as the ratio of the sample absorbance to the cut-off absorbance and multiplied by 10 (absorbance of sample/mean absorbance of cut-off ×10).