The causes of low neutrophils include decreased neutrophil production, maturation disorders, immunologic factors, and abnormal distribution of neutrophils. 1. Decreased neutrophil production (1) Certain cytotoxic drugs and chemical poisons can affect cell division, such as cytarabine, interfering with protein synthesis and cell replication; (2) Blood system diseases such as aplastic anemia, etc., neutrophil granulocyte production disorders caused by reduced indicators. 2. Maturation disorders: folic acid and vitamin B₁₂ deficiency, myelodysplastic syndromes, etc., leading to malformation of differentiated mature granulocytes, or the emergence of ineffective hematopoiesis and so on. 3. Immune factors: such as systemic lupus erythematosus, rheumatoid arthritis, etc., leading to the destruction of neutrophils by the immune system after combining with antigen-antibody complexes. 4. Abnormal distribution of neutrophils: the neutrophil circulating pool is reduced and transferred to the marginal pool, and the total number of neutrophils remains unchanged, which is called pseudo-reduction. Unexplained low neutrophils need to be examined in regular hospitals and treated under the comprehensive evaluation of physicians.