ASCP International (ASCPi) Practice Exam 2026 - Free ASCPi Practice Questions and Study Guide

The postzone effect happens when there is too much antigen relative to antibody in a serologic test, so there aren’t enough antibodies to cross-link antigens and form visible complexes. The remedy is to add more antibodies, which increases the potential for cross-linking and allows lattice formation to occur, producing a detectable reaction. Diluting the serum would address antibody excess (the prozone effect), not postzone. Using a higher antigen concentration would worsen the imbalance. Re-testing later won’t fix the immediate antigen–antibody ratio issue. So, increasing the antibody amount directly targets the imbalance causing the false-negative result.