Can a blood routine test detect viral or bacterial infections

Blood routine can preliminarily distinguish between viral and bacterial infections, but cannot directly diagnose them. Blood routine mainly provides clues through changes in indicators such as white blood cell count, neutrophil ratio, and lymphocyte ratio. Viral infections usually manifest as normal or decreased white blood cells accompanied by an increased proportion of lymphocytes, while bacterial infections often result in an increase in both white blood cell and neutrophil proportions. During viral infection, the blood routine may show normal or mild decrease in white blood cell count, relative increase in lymphocyte proportion, and normal or decreased neutrophil proportion. For example, viral diseases such as the common cold and flu often exhibit this pattern. Partial viral infections such as EB virus may lead to an increase in the absolute value of lymphocytes, but overall lymphocytes are still predominant. This type of situation usually does not require antibiotic treatment and relies mainly on symptomatic support, but requires a comprehensive judgment based on clinical symptoms and other examinations. During bacterial infection, the blood routine usually shows a significant increase in the total number of white blood cells, a significant increase in the proportion of neutrophils, and possible left shift of the nucleus, while the proportion of lymphocytes is relatively reduced. Bacterial infections such as Streptococcus pneumoniae pneumonia and acute suppurative tonsillitis often present with such symptoms. However, certain special bacterial infections such as typhoid fever may manifest as leukopenia, while severe bacterial infections combined with immune suppression may not show typical changes. At this point, it is necessary to combine inflammatory markers such as procalcitonin and C-reactive protein to assist in diagnosis. The results of the blood routine test should be interpreted by the doctor in conjunction with the patient's medical history, physical examination, and other laboratory tests. Relying solely on blood routine to distinguish infection types has limitations, and specific tests such as pathogen culture and nucleic acid testing may be necessary when necessary. If there is persistent fever or worsening of the condition, timely follow-up should be sought to avoid self administering antibiotics based on blood routine results.