The hook effect occurs when high levels of an analyte in a sample (e.g., human chorionic gonadotropin (hCG) in twin pregnancies) interfere with the antigen-antibody reaction in an immunoassay, resulting in a falsely negative result. Quantifying the amount of hCG is essential in diagnosing pregnancy, and the hook effect can pose a diagnostic challenge in twin pregnancies where hCG levels can be significantly elevated.
