When determining whether a child's cold is caused by a viral infection or a bacterial infection, you can take the child to the hospital for a routine blood test. In most cases, it is caused by a viral infection. Combined with the routine blood test, if there is an increase in white blood cell count and neutrophil count, it usually indicates a bacterial infection.

If the white blood cell count is normal, or low, along with an increase in lymphocyte count or percentage, it usually indicates a viral infection. Alternatively, combining this with a C-reactive protein test, if the C-reactive protein level significantly multiplies, then it indicates a bacterial infection.