Usually when you get a routine blood test, doctors look at three main data: white blood cell count (WBC), lymphocyte percentage and neutrophil percentage, while the WBC count is often referred to as the blood picture, the latter two are the classification of white blood cells. As we all know, white blood cells are the body’s “guards”, specializing in helping the body to defend itself against foreign invasion such as bacteria. However, among these guards, there is a team of “elite soldiers” that needs more attention, and that is neutrophils. Neutrophils are always at the forefront of the battle and play a pivotal role in the body’s immune system. For doctors, blood tests are not just about whether white blood cells are below normal, but also about the number of neutrophils. What are neutrophils? Neutrophil (neutrophilic granulocyte) is a colorless or very pale reddish cytoplasm with many diffuse, small (0.2 to 0.4 microns) light red or light purple granules in a Wright’s stained blood smear. The nucleus is rod-shaped or 2-5 lobed, with thin filaments connecting the leaves to each other. Its granule surface is wrapped with a membrane and can be divided into 1 to 4 types. The granules contain myeloperoxidase (myeloperoxidase), acid phosphatase, phagocytin (phagocytin), lysozyme, β-glucosidase, alkaline phosphatase, etc. Neutrophils play a very important role in the non-specific cellular immune system of the blood, being in the first line of defense of the body against microbial pathogens, especially in the invasion of septic bacteria, and being attracted to the site of inflammation by chemotactic substances when inflammation occurs. Since they obtain energy by glycolysis, they are able to survive in hypoxic conditions of swelling and poor blood flow, where they form a cytotoxic presence that destroys the cell membranes of bacteria and nearby tissues. Since neutrophils contain a large number of lysosomal enzymes, they are able to break down bacteria and tissue fragments that are engulfed into the cells, so that invading bacteria are enclosed in a localized area and destroyed, preventing the spread of pathogenic microorganisms in the body. When the neutrophils themselves disintegrate, the release of each lysosomal enzyme class can dissolve the surrounding tissue and form an abscess. Neutrophils are one of the routine blood tests, but do you know how to read a routine blood test? When you get a blood test, the patient is usually at a loss as to what the dense data means. Especially when you see a few elevated or decreasing arrows, you are scared inside, wondering if the problem is serious. If the white blood cell count is higher than 10,000, inflammation is more powerful, anti-inflammatory drugs and suspensions can be used, and the white blood cell count is lower than 4,000, which means that resistance is lower and antipyretics, etc., should be used sparingly. If the percentage of lymphocytes is high, it is a viral infection; if the percentage of neutrophils is high, it is a bacterial infection. Leukocytes are mainly neutrophils, and a high neutrophil count is usually associated with a high white blood cell count, which is commonly associated with infections, usually caused by colds. A cold can cause an increase in neutrophil percentage. If the white blood cell count and neutrophil percentage are both high, it is a bacterial infection; if the white blood cell count is low and the lymphocyte percentage is high, it is a viral infection; if the white blood cell count is normal or low and the neutrophil percentage is high, there may be both a viral and a bacterial infection. Of course, this is the basic method of judgment, and the specific situation needs to be determined by the doctor.