Cold and flu blood test reports to see whether it is a viral or bacterial infection can usually be determined by the values of white blood cells, neutrophil ratio, C-reactive protein, lymphocyte ratio, monocyte ratio and so on. In clinical practice, routine blood tests are usually required after a cold. If there is an increase in leukocyte or neutrophil ratio, or one of them, the possibility of bacterial infection is higher. In addition, the C-Reactive Protein (CRP) value can also be taken into account. If the CRP value is significantly elevated, it usually indicates the presence of a bacterial infection as well. If the lymphocyte or monocyte ratio is elevated and the white blood cells or neutrophils are normal, a viral infection is usually present. In some cases, however, both bacterial and viral infections may be present at the same time. It is important to seek medical attention to identify the cause of the cold and to treat it appropriately under the guidance of your doctor.