Hook's effect - a rare presentation in HBsAg screening.

Detection of Hook's effect, the false negative results in HBs Ag immunoassay screening. Two drops of donor's serum was added to the sample well of hepacard device using a dropper and was allowed to react for 20 minutes and results read thereafter. The hepacard device when read after 20 minutes showed only one distinct pink test line and no control line. Serial dilutions (1:10, 1: 20) of the donors sample in normal saline was done and the test was re-run. Sample in 1: 10 dilution showed both control and faint pink test line, which intensified to pink band in 1: 20 diluted sample. The goal in the immunoassay detection of HBsAg should be to minimize erroneous results; so as not to endanger patient health and the blood supply.