Depressive disorders generally have no obvious organic lesions, blood tests can not diagnose depression, but can play a role in ruling out other diseases, such as ruling out secondary mood disorders caused by organic brain diseases, somatic diseases, certain drugs and psychoactive substances. 1. Organic brain diseases: for example, intracranial degenerative diseases, cerebrovascular disease, intracranial infection, traumatic brain injury, brain tumor, epilepsy and so on. Such as Alzheimer’s disease need to check the routine biochemistry, thyroid function measurement, vitamin B12 and folic acid test, complete blood count and serum syphilis antibody test. 2. Physical disease: physical infection, internal organ disease, endocrine disorders. For example, benign parathyroid adenoma in abnormal parathyroid function causes hypercalcemia and mental symptoms. 3. Certain drugs and psychoactive substances: such as barbiturates, alcohol, amphetamines, cocaine, ketamine, opioids, tobacco and other mental disorders caused by laboratory tests have the corresponding index changes. It should be reminded that, for patients with depression, it is recommended that family members accompany the patient to the hospital for standardized diagnosis and treatment, so as not to delay the condition, resulting in adverse consequences.