Abstract: Objective To investigate the diagnostic efficiency of high fluorescence intensity cell value (HF-BF) of tumor cells in pleural fluid and ascites for cancer by XE-5000 hematology analyzer. Methods Eighty pleural fluid and ascites specimens were collected from inpatients in the First Hospital of Lanzhou University from May 2017 to May 2018, including 44 males and 36 females with age ranging from 21 to 88 years. Of the 80 cases, there were 40 non-malignant specimens, including 11 cases of cirrhosis, 7 cases of pulmonary heart disease, 6 cases of pneumonia, 6 cases of other digestive tract diseases, 2 cases of chronic renal failure and 8 cases of other diseases; And another 40 malignant specimens included 19 cases of lung cancer, 6 cases of liver cancer, 6 cases of breast cancer, 2 cases of ovarian cancer, 2 cases of bladder cancer and 5 cases of other malignant tumors. XE-5000 hematology analyzer was applied to detect HF-BF of the 80 specimens, and the optimal threshold of HF-BF to diagnose malignant tumor were determined by ROC curve. Results The range of HF-BF value in malignant pleural fluid and ascites was 35×10⁶/L to 2 892×10⁶/L with the median of 88×10⁶/L, and it was 0 to 34×10⁶/L (median, 14.5×10⁶/L) in non-malignant pleural fluid and ascites, with statistically significant difference (P=0.042); however, there was no significant difference in the percentage of high fluorescence intensity cells (HF-BF%) between the two groups (P=0.246). The area under ROC curve of HF-BF of tumor cells in pleural fluid and ascites was 0.632, and the optimal diagnostic threshold was 39.5×10⁶/L with the sensitivity, specificity of 65% and 67.5%, respectively. Conclusion HF-BF can be used as a screening index for malignant pleural fluid and ascites. Positive samples should be further diagnosed combining the results of biochemistry tests of pleural fluid and ascites, exfoliated cell examination, tumor markers and radiography.