BACKGROUND: After the patient had a long course of disease and symptoms of bilateral breast milk secretion, the doctor first considered that the patient had breast cancer. After screening and excluding the breast, he found that the patient had high prolactin, and suspected that the patient had a pituitary tumor. After breast cancer and pituitary adenoma were excluded, the doctor suspected that there might be interference of macroprolactin. After PEG treatment, we also excluded the interference of macroprolactin. After repeated communication with doctors and patients, we found that the patient had gone to a psychiatric hospital for treatment and taken the antidepressant drug Deanxit (Flupentixol and Melitracen tablets). METHODS: Flupentixol acts by antagonizing hypothalamic prolactin releasing inhibitory factors, reducing dopamine release, leading to hyperprolactinemia. RESULTS: The patient's examination found that prolactin was 3,172.9 mIU/L (normal range 108.80 - 557.10 mIU/L), and after PEG treatment, it was 2,692.86 mIU/L. Patient stopped using Deanxit for one month, and prolactin levels were 302.8 mIU/L. CONCLUSIONS: Only effective communication between laboratory and clinical departments can make laboratory results more accurate and provide strong guarantees for clinical diagnosis and treatment.