Final answer:
Anti-Lua is often undetected in routine screening because it's a rare antibody with weak reactivity and is not included in standard blood testing panels unless there's a known risk. Sensitive tests are required to detect it.
Step-by-step explanation:
The anti-Lua antibody can go undetected in routine testing because it typically has a low frequency of occurrence and a generally weak reactivity. Routine blood transfusion screening does not always include testing for the Lua antigen, mainly due to its rarity and the fact that most individuals do not have antibodies against it. As a result, the Lua antigen is not part of the standard panel of tests unless the individual has a history of forming antibodies or is known to be at risk.
Furthermore, the methods used for routine antibody screening may not be sensitive enough to detect the weak reactions caused by an anti-Lua antibody. This is why specialized or more sensitive testing procedures, such as enzyme-treated or low ionic strength saline-enhanced tests, are necessary to detect such antibodies when there is a clinical indication or a suspected case of alloimmunization.