Leukocyte 2.9 means that the total number of white blood cells is 2.9 x 10⁹/L, which is lower than normal and is abnormal. The condition is relatively severe and the severity is highly dependent on the cause. Common causes include viral infections such as influenza, autoimmune diseases such as systemic lupus erythematosus, and hematologic diseases such as aplastic anemia. 1. Viral infections: Infection is the most common cause of leukopenia, especially viral infections such as influenza, chickenpox and so on will cause a decrease in the total number of white blood cells. If the total number of white blood cells is 2.9×10⁹/L, the condition is relatively serious, but the condition can be cured after active and standardized treatment, and the drugs include acyclovir and so on. 2. Autoimmune diseases: such as dry syndrome, systemic lupus erythematosus, etc., due to the production of antibodies in the body and the secretion of negative hematopoietic regulatory factors by lymphocytes, so that the production of white blood cells is reduced and destruction is increased, resulting in a decrease in the total number of white blood cells. The course of the disease is long and cannot be cured, and the condition is relatively serious. 3. Blood system diseases: such as aplastic anemia, acute leukemia, etc. can cause a decrease or inhibition of leukocyte production, resulting in a decrease in the total number of white blood cells. The condition is more serious, and if the condition progressively worsens, the only cure is hematopoietic stem cell transplantation. There may be other reasons for the decrease of white blood cells, such as typhoid fever, hypersplenism, etc. When you find that the total number of white blood cells decreases, you should actively find out the reasons and standardize the treatment under the guidance of your doctor, so as not to aggravate the condition and delay the treatment.