High cytokeratin 19 fragment in pleural fluid is an abnormality in body condition, the corresponding indexes mainly come from epithelial cells, the reasons for the rise of corresponding indexes in pleural fluid mainly include lung cancer and pneumonia, and it may also be caused by breast cancer. 1. Lung cancer: mainly for non-small cell lung cancer, the rise of corresponding tumor markers in pleural fluid and the obvious rise of indicators are highly suggestive of lung cancer, which needs to be combined with CT examination. 2. Pneumonia: slight increase of corresponding indicators, accompanied by pleural fluid may be correlated with pneumonia, accompanied by symptoms of cough and fever, and the corresponding indicators can be reduced through treatment. 3. Breast cancer: when breast cancer invades the pleura, pleural effusion can occur, when breast cancer can cause cytokeratin 19 fragment elevation, common symptoms are painless lumps in the breast, invading the pleura can have chest pain. If the cytokeratin 19 fragment of pleural fluid is high, accompanied by obvious cough and chest pain, it is necessary to consult a doctor in time for observation, diagnose the corresponding cause of the disease through CT examination, and carry out standardized treatment under the guidance of clinicians to avoid delaying the condition.