The Chlamydia trachomatis antibody detection test diagnoses infections when pathogens are no longer detectable in swabs. Particularly useful for Lymphogranuloma venereum infection caused by C. trachomatis detecting systemic antibody responses, aiding in inguinal disease diagnosis. Healthcare professionals use this indirect method to diagnose chronic or invasive infections and post-infectious complications, such as sexually acquired reactive arthritis (SARA).