Leukocytes 2.5×10^9/L can be seen in a variety of diseases, and the exact length of time it takes to return to normal needs to be analyzed according to the original disease. The normal range of leukocytes is (4-10)×10^9/L. Leukocytes 2.5×10^9/L is a mild case of leukopenia. In clinical cases, leukopenia can be caused by a variety of conditions. For leukopenia induced by cold or medication, the leukocytes can start to return to normal gradually after the cold symptoms are relieved or the medication is stopped, which takes about 1 week. If the decrease is clearly caused by a virus, it usually recovers gradually within 2 weeks. In the case of malignant diseases of the hematological system, which are relatively more difficult to deal with, such as chronic leukemia and myelodysplastic syndrome, recovery to normal levels may not be possible. Therefore, patients with leukocytes of 2.5×10^9/L need to actively visit the hospital’s Infectious Diseases Department and be treated accordingly by a professional doctor who can clarify the cause.