Keratin 19 is a cytokeratin 19 fragment, and its bias is 0.4 to be important. Cytokeratin is a structural protein within the epithelial cells and is a component of the cytoskeleton; cytokeratin 19 fragment is the fragment of keratin contained in alveolar epithelial cells when they apoptose, and the fragments of the keratin contained in their cells are degraded into soluble substances and enter into the bloodstream, making the blood level increase. The normal value of cytokeratin 19 fragment <3.3ng/ml can be used to assist in the diagnosis of non-small cell lung cancer, and is also important for monitoring the efficacy and prognosis of non-small cell lung cancer. When cytokeratin 19 fragment is high, it indicates that apoptosis of alveolar epithelial cells is increased, and there may be tumors, metastatic foci, or recurrence of the patient, but cytokeratin 19 fragment is not a specific diagnosis, and other auxiliary tests should be carried out to confirm the diagnosis under the guidance of the doctor. When the cytokeratin 19 fragment is 0.4 high, you should seek medical attention in time to clarify the diagnosis and carry out auxiliary examinations under the guidance of a doctor to avoid delaying the condition.