Chicken red blood cells (RBCs) are commonly used in hemagglutination inhibition (HI) tests to
measure hemagglutinating antibodies against influenza viruses. The use of horse RBCs in the HI test can reportedly
increase its sensitivity when testing human sera for avian influenza antibodies. This study aims to compare the
proportion of positives detected and the agreement between two HI tests using either chicken or horse red blood
cells for antibody detection in sera of ducks experimentally infected or naturally exposed to Indonesian H5 subtype
avian influenza virus. In addition, comparison with a virus neutralisation (VN) test was conducted with the
experimental sera.