Viral infection: A mild to moderate elevation in WBC count with a normal differential can often be seen in viral infections, which are common and typically self-limiting. The body's response to a viral infection can cause a slight increase in white blood cell count as part of the immune response.

Bacterial infection: Early stages of bacterial infections can present with a mildly elevated WBC count and a normal differential. As the infection progresses, the differential may become more abnormal, showing an increase in specific types of white blood cells.
Inflammatory conditions: Conditions such as rheumatoid arthritis, inflammatory bowel disease, or other autoimmune diseases can cause a mild elevation in WBC count due to the body's inflammatory response.
Stress or exercise: Physical stress, including intense exercise, or psychological stress can lead to a transient increase in WBC count due to the release of stress hormones like cortisol and adrenaline.

Severe bacterial sepsis: Although the differential is currently normal, severe bacterial sepsis can initially present with a mild elevation in WBC count before progressing to more severe abnormalities. It is crucial to monitor the patient closely and consider this diagnosis, especially if the patient's condition worsens or if there are other signs of sepsis.
Leukemia (early stages): In the early stages of leukemia, the WBC count may be only mildly elevated, and the differential may appear normal or near-normal. This diagnosis is critical to consider because of its significant implications for treatment and prognosis.
HIV infection: Acute HIV infection can cause a mild increase in WBC count with a normal differential. Given the importance of early diagnosis and treatment of HIV, this should be considered in the differential diagnosis, especially in high-risk individuals.

Myeloproliferative neoplasms: These are rare disorders that affect blood cell production in the bone marrow and can cause an elevation in WBC count. Examples include polycythemia vera, essential thrombocythemia, and primary myelofibrosis.
Lymphoma: Certain types of lymphoma can present with a mild elevation in WBC count and a normal differential, although this is less common.
Parasitic infections: Some parasitic infections, such as those caused by worms or protozoa, can lead to an increase in WBC count as part of the body's immune response. These infections are less common in many parts of the world but should be considered in travelers or individuals with specific risk factors.