Final answer:
A false positive on inhouse EG testing can occur due to cross-reactivity, where epitopes from a different pathogen are similar to those found on the pathogen being tested for.
Step-by-step explanation:
A false positive on inhouse EG testing can occur due to cross-reactivity, where epitopes from a different pathogen are similar to those found on the pathogen being tested for. This can lead to a positive result even when the infection or condition is actually absent. False positives are common in antibody-based tests, such as ELISA, which are often used as screening tests. If a false positive is obtained, confirmatory tests like immunoblot or nucleic acid tests are used to verify the result.