The beryllium test—most commonly performed as the Beryllium Lymphocyte Proliferation Test (BeLPT)—is a specialized immunological assay used to evaluate sensitization to the toxic metal beryllium. Exposure primarily occurs in industries such as aerospace, electronics, and metal machining. The assay measures how a patient's white blood cells react when exposed to beryllium salts in a laboratory setting. A positive proliferation response indicates cellular sensitization, which serves as a crucial diagnostic marker for chronic beryllium disease (CBD). Early detection enables clinicians to monitor lung health, manage occupational exposure risks, and implement timely interventions before irreversible pulmonary fibrosis develops.