The traditional approach to distinguish between viral or bacterial infections is to test the blood routine, and the WBC count of peripheral blood cells and also the percentage of neutrophils in the blood routine are often used clinically as one of the traditional screening tools to determine whether a bacterial infection is present. A low or decreased white blood cell count and an increased lymphocyte count or percentage suggests a viral infection. An elevated white blood cell count and neutrophil count or percentage suggests a bacterial infection. In fact, blood tests are not very good at distinguishing between bacterial and viral infections. For example, a reduced white blood cell count may be a sign of a serious bacterial infection, and an increased white blood cell count and neutrophil count or percentage may not necessarily be a bacterial infection. The use of peripheral blood leukocyte count and neutrophil percentage alone as a screening tool for bacterial or viral infections is neither sensitive nor specific. The same is true for acute response markers such as sedimentation, C-reactive protein, and serum calcitoninogen, none of which can be used alone or in combination to distinguish between bacterial or viral infections, nor are they good predictors of the presence of a serious bacterial infection.