White blood cell 2.9×10⁹/L is not normal in elderly. The normal value of white blood cells in adults is (4~10)×10⁹/L, and the value of white blood cells in the elderly is 2.9×10⁹/L, which belongs to the lowering of white blood cells, and it is common in the infections, hematologic diseases, physical and chemical injuries, and rheumatoid arthritis. 1. Infection: it may be caused by viral infection or serious bacterial infection, common diseases such as measles, hepatitis B, typhoid fever and paratyphoid fever. 2. Blood diseases: such as aplastic anemia, leukemia, myelodysplastic syndrome, granulocyte deficiency and other blood diseases. 3. Physical and chemical injuries: long-term X-ray irradiation, drug use such as vinblastine, antipyretic and analgesic drugs such as indomethacin, and so on. 4. Rheumatoid arthritis: the elderly rheumatism, rheumatoid arthritis, there will also be a decrease in white blood cells. If there is an abnormal result of 2.9×10⁹/L white blood cells in the elderly, it is recommended to consult a doctor in time to clarify the cause of the disease with the help of the doctor and carry out targeted treatment.