Final answer:
The white blood cell count with differential results for the febrile 3-year-old boy shows leukocytosis with neutrophilia and lymphopenia, which suggests an increased white blood cell count, specifically of neutrophils, and a decrease in lymphocytes, indicating a possible bacterial infection.
Step-by-step explanation:
The white blood cell count with differential for the febrile 3-year-old boy indicates a total white blood cell count of 22,100/mm3, which is above the typical 'healthy' range for white blood cells (3.5 to 11 x 109 cells/L). This condition is known as leukocytosis, which is an increased number of white blood cells in the blood, often suggestive of an infection or inflammation.
The differential count shows neutrophilia, with neutrophils at 75% (normal range 50-70%) and bands at 15% (normal 0-4%), both of which are elevated. Neutrophils are the predominant type of granulocyte and a principal component of the innate immune response, and an increased proportion typically indicates a bacterial infection. Band cells, which are immature neutrophils, are often elevated when there is an increased demand for neutrophils.
There is also evidence of lymphopenia, with lymphocytes at 4% (normal range 30-40%), which is lower than the normal range. Lymphocytes are a type of white blood cell that is part of the adaptive immune response, and a decrease may occur in response to severe infections.
Therefore, the best description of this child's WBC with differential results is leukocytosis with neutrophilia, indicating an increased white blood cell count, specifically of neutrophils, which is often suggestive of bacterial infection requiring medical attention.