Low-incidence antigens are not usually found on screen cell and antibody panels.
Antibodies are hard to test for, but it is usually not difficult to find compatible blood.
Suspect this antibody if an AHG crossmatch is incompatible and other causes have been ruled out, such as a positive donor DAT or ABO incompatibility.
Examples of low-incidence antigens include: Cw, V, Kpa, Jsa.
When going through the process of Ruling Out, antibodies like anti-V, anti-Cw, anti-Lua, anti-Kpa, and anti-Jsa usually fall into the "unable to rule out" category.