In adults, normal CD4 counts range from 500 to 1,200 cells per cubic millimeter of blood, reports Lab Tests Online. CD4 cells are white blood cells that fight infection, explains WebMD. Doctors use CD4 counts to evaluate the health of the immune system and monitor human immunodeficiency virus progression.
CD4 counts are usually higher in the evening and lower in the morning, according to Lab Tests Online. Illnesses such as influenza, pneumonia and herpes simplex viral infection can temporarily lower CD4 counts. HIV targets CD4 cells; in general, normal CD4 counts indicate that an HIV infection has not affected the immune system, and lower-than-normal CD4 counts indicate that the infection is progressing. Patients with CD4 counts below 200 cells per cubic millimeter of blood are diagnosed with acquired immunodeficiency syndrome, or AIDS.