The Chlamydia Trachomatis Antibody (IgG) (CHLAG) Test is a blood test that detects Immunoglobulin G (IgG) antibodies against the C. trachomatis bacteria, indicating a past or ongoing infection, not necessarily a current, active one, as these antibodies remain in the blood long after treatment. While useful for screening (like for infertility) or understanding exposure history, it’s often combined with Nucleic Acid Amplification Tests (NAATs) for pinpointing active infections, as IgG alone can’t distinguish past from present, but high levels might suggest recent or significant infection