The causes of high cytokeratin may be pneumonia, tuberculosis, and tumor. 1. Pneumonia: Mildly elevated cytokeratin may occur due to inflammation that stimulates the epithelial cells. 2. Tuberculosis: tuberculosis may also stimulate the epithelial cells and cause mildly elevated cytokeratin. 3. Tumor: Cytokeratin 19 fragment is the preferred tumor marker for non-small cell lung cancer, with the highest positivity rate in squamous cell carcinoma. In addition, breast cancer, bladder cancer, colorectal cancer, prostate cancer, etc. may also show elevated cytokeratin. There may be other reasons for high cytokeratin, so it is recommended to go to the hospital in time to identify the cause of the disease and then give targeted treatment.