Cytokeratin is one of the tumor markers with relatively high specificity for tumors such as cervical cancer, squamous lung cancer and squamous head and neck cancer. The normal range varies slightly depending on the normal range set by the laboratory in different medical institutions, and is usually 0-3.3 ng/mL. If this indicator is only elevated in normal patients, it may be related to the presence of lung infections and certain skin diseases. If the index continues to rise, patients should see a specialist oncologist for further treatment and evaluation of relevant tests, in conjunction with changes in the levels of other tumor markers and the corresponding imaging guidance.