immunoglobulin (IVIG)[1]. As stated by the authors, this phenomenon, despite already largely described, remains too often unconsidered by prescribers. IVIG administration complicates serological profile interpretation at the laboratory level, as the biologist is most often unaware of such treatment, but also misleads the clinician who may falsely interpret the laboratory results. Noteworthy, one should highlight that any diagnostic assay based on an immunological reaction could potentially be disrupted by IVIG as they may contain any antibody found in the general population. IVIG are prepared from a pool of around 1000 blood donations and therefore reflect in their constitution the serological status of the donor population. Depending on the manufacturer, blood collection may be obtained from donors with different selection criteria that will translate into different IG composition. In 2014 in our institution, 682 patients had received around 220 kg IVIG for a cost of 8 million€ mostly for immune mediated neurological disorders or in organ transplantation setting. IVIG administration has been increasing for the past years, and we recently tested several lots of IVIG from 2 different manufacturers (Table 1). Residual volume of IVIG was collected from perfusion systems after patient’s infusion and tested for virus serological markers on our routine diagnostic system (Architect, Abbott, Rungis, France or Liaison-XL, DiaSorin, Antony, France) both pure and after a 1/10 dilution in saline buffer. Strikingly, all IVIG lots were highly positive for all tested antibodies (Ab) except hepatitis B core (anti-HBc) Ab. Indeed, anti-HBc Ab were only found in Privigen but never in Clairyg IVIG. The former, produced by CSL Behring, uses blood donations from several countries and follows an international regulation, whereas the second, produced by LFB exclusively on French blood donations, follows European rules. Our data reinforce those recently reported by Bright et al.[2]. Most Ab were still detected after a 1/10 dilution; this relatively high concentration likely explains why they may still be detected in patient’s serum after infusion. IVIG half-life is between 3 and 4 weeks, and a 4-month delay should be respected to avoid any misinterpretation of a serological profile. As highlighted by several recent publications, misinterpretation of serological profiles may have deleterious consequences and clinicians should be more sensitized on this issue [2–4]. On the specific issue of hepatitis B and beside transfer of anti-HBc Ab, one should also emphasize the risk of masking hepatitis B surface antigen (HBsAg) detection by hepatitis B surface antibody (anti-HBs)