Relationships between pleural fluid pH, PCO2 to pleural fluid PO2, amylase, protein, glucose and white cells in tuberculous and malignant effusions.

The relationships between pleural fluid pH and PO2 to pleural fluid PO2, amylase, protein, glucose, white cell count were examined in 110 cases of tuberculous and 140 cases of malignant pleural effusions. Pleural fluid amylase concentrations of 200 or more units/ml indicated malignant effusions rather than tuberculous effusions with a specificity of 92.7 per cent and sensitivity of 27.1 per cent. There was evidence which suggested that the increasing pleural fluid amylase concentrations were due to the excessive leakage of serum amylase into the pleural cavity secondary to the break-down of capillaries by tuberculosis and malignancy as well as the production of amylase by tumor cells invading the pleura. The decreasing pleural fluid pH and increasing pleural fluid PCO2 had a significant linear relationship with decreasing fluid PO2, increasing pleural fluid protein and decreasing fluid glucose. These indicated a leakage of serum protein into the pleural cavity and the over-utilization of glucose relative to the transport defect of low pleural fluid glucose concentrations in the acidotic fluid of tuberculous and malignant effusions. No relationship between pleural fluid pH and PCO2 to pleural fluid and white cell count was found in the present study.