A false reactive hepatitis B surface antigen result due to dislodged gel from Vacutainer

Preanalytical variables play a key role in the correctness of laboratory test results. We report a false reactive result for hepatitis B surface antigen (HBsAg) on serological testing with a relatively low OD. The pilot sample was collected in yellow top BD Vacutainer^® (SST™ II Advance 5 mL tube) with separator gel and was marked for serological testing. It was centrifuged at 7000 rpm for 30 min. Serological testing was performed by chemiluminescence on Abbott Architect Plus i1000SR with Abbott kits for HBsAg, anti-HIV, and anti-HCV. This particular sample tested reactive for HBsAg with S/CO of 1.91, S/CO for HBsAgQ2NC (Negative kit control) being 0.19 and that of HBsAgQ2PC (Positive kit control) being 3.65. Repeat testing from the same Vacutainer was also reactive for HBsAg with S/CO of 2.10. Nucleic acid testing was performed and was found to be nonreactive. We repeated serological testing with a sample from fresh frozen plasma of the same donor unit. It was nonreactive. Cross contamination was ruled out by repeat testing of two serial samples before and after this unit number. The serum showed an unusual appearance on visual inspection after centrifugation. By exclusion, we concluded that the gel probably got partially dislodged into the serum, giving a relatively low reading and false reactive result for HBsAg. This highlights the possibility of inert gel not always being inert, the importance of repeat testing from a different sample in case of low reading, the importance of visual inspection, a need for manufacturers and laboratory personnel to consider such preanalytical variables which, though not much mentioned in literature, can affect test results. These results have a multi-fold impact on the donor or patient's mindset, treatment outcome and/or fate of blood donation. These are definitely preventable if more such guidelines are made available for handy reference in handling such results.