When blood is drawn for a cold, it is usually a routine blood test and a C-reactive protein, which are the two most commonly used to see whether the overall symptoms of the cold are mild or severe. For infections with specific pathogens that may cause more serious manifestations, it is possible to see from this aspect. First, look at the C-reactive protein, if it reaches more than 50mg/L or even 100mg/L, the systemic inflammatory response is very obvious and should be taken seriously. Secondly, look at the white blood cell count in the blood routine. If it is a bacterial infection, the neutrophils will be mainly elevated and the white blood cell count will rise along with it. If the elevation exceeds 15 x 10^9 cells/L or even reaches 20 x 10^9 cells/L or more, you need to look for an associated focus of infection and will likely need to apply to antibiotic therapy. In the case of a viral infection, the white blood cell count is likely to be slightly elevated or in the normal range due to an increase in the lymphocyte count. Again, look at the platelet count. Specific diseases or severe infectious diseases can significantly deplete platelets and the platelet count will drop, and if the drop is relatively rapid and particularly large, it is likely to lead to systemic bleeding.