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In children, there is usually a presence of high lymphocytes. But in your child, absolute lymphocytosis is present. Hence, your child should be referred to a hematologist for examination, especially, lymph nodes palpation, liver, and spleen palpation. (If needed, USG scan can be done for that). Tuberculosis, measles, chickenpox, hepatitis, infectious mononucleosis, brucellosis, etc., are some of the infective causes but specific symptoms regarding that are not present as per history. Autoimmune disorder and leukemia also are some of the causes. These are different causes to provide you information regarding lymphocytosis cause.
Your latest smear report shows high atypical lymphocytes (attachment removed to protect patient identity), mostly it can be some form of viral infection. But we do not want to take the risk and consult to a Hematologist for examination and investigate with USG abdomen scan also. If needed, then flow cytometry like higher investigation can be planned. Hope this provided information will be beneficial to you while you consult a nearby hematologist for examination. Take care.
For more information consult a hematologist online --> https://www.icliniq.com/ask-a-doctor-online/hematologist