Firstly, can CBC tests distinguish between bacterial or viral infections?
Simply, the answer is no. Literally, not only CBC tests can not differentiate between types of infections, there is no test that can absolutely differentiate between bacterial or viral infections, including the "gold standard" of blood cultures. A positive result of blood cultures does not mean a systemic inflammatory of infection, while a negative result does not negate the presence of an infection.
Secondly, do child with a fever need routine CBC test?
The answer to this question is much more complex. We need to clarify the sensitivity and specificity of CBC tests for determining the type of infection in febrile patients. For focal infections, that such as skin boils and carbuncles or traumatic oozing, which are obvious signs of bacterial infection, or the clinical manifestations clearly point to a common viral influenza, there is no need to take CBC tests to determine the types of infection.
However，for children whose fever is the only clinical symptom, routine CBC tests are needed,especially white blood cell count (WBC) and neutrophil count and granulocyte count included. In summary of the available studies, we believe that WBC is superior to clinical assessment alone for determining bacterial infections, especially for screening of severe bacterial infections in children under 3 months of age.
In fact,its specificity is poor, since in addition to serious bacterial infections, viral infections as well as non-infectious inflammatory conditions can elevate white blood cells.Therefore, we recommend that newborns less than 29 days with fever need to have not only routine CBC tests, but also other further laboratory tests. infants within 1-3 month need to have CBC tests completed, but CBC tests are not routinely recommended for children over 3 months of age.
Whether to take the CBC test or further testing needs to be weighed against the certain circumstances of children, and the results should be analyzed in quite particular situations, rather than simply denying the significance of a particular test.
