A routine blood test for a child with a fever can look for bacterial and viral infections, as well as anemia, and most often for white blood cells, which are high enough to indicate a bacterial infection. The specific categories of white blood cells include neutrophils, monocytes and lymphocytes. An increase in neutrophils is also associated with an increase in white blood cells, which also indicates a bacterial infection, while an increase in lymphocytes and monocytes mostly indicates a viral infection. In addition to white blood cells, you can also look at red blood cells and hemoglobin, which are indicators of anemia, but during an infection, sometimes a low hemoglobin does not mean that the child is anemic and is considered to be related to the infection. When the infection is under control, the hemoglobin may be normal when the routine blood tests are repeated.