Leukocyte 2.9 precisely means that the number of peripheral blood leukocytes is 2.9×10⁹, which is low relative to normal and falls within the abnormal range. The normal value of leukocytes is (4~10) x 10⁹, which is an important participant in the body’s immune mechanism and helps the body to remove inflammatory factors formed by various bacteria, viruses and other infections. There are various conditions that cause leukopenia, as shown below: 1. Gram-negative bacillus infections (typhoid fever, paratyphoid fever, etc.). 2. Viral infections (influenza, chicken pox, rubella and viral hepatitis). 3. Blood system diseases (aplastic anemia, severe megaloblastic anemia and myelodysplastic syndromes, etc.). 4. Physical factors (X-rays, γ-rays and other radioactive environmental factors). 5. Chemical factors (benzene, lead, mercury, chloramphenicol and sulfonamides, etc.). 6. Autoimmune diseases (such as systemic lupus erythematosus) produce autoantibodies that affect the function of white blood cells. 7. Increased leukocyte swallowing due to hypersplenism. In summary, the white blood cell count of 2.9×10⁹ belongs to the low white blood cell, and there are various reasons for it. The low white blood cell count should be further examined in time to find the cause of the disease, and targeted treatment should be carried out, while avoiding all the easy infection factors to prevent the infection from prolonged and unresolved.