Low Glucose and pH Levels in Malignant Pleural Effusions: Diagnostic Significance and Prognostic Value in Respect to Pleurodesis

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Abstract
In order to determine the diagnostic and prognostic significance of low pleural glucose and pH levels, we executed a prospective study of these parameters and cytologic yield in 77 cases of malignant pleural effusions diagnosed from 116 consecutive thoracoscopies. The extension of the neoplasms detected by thoracoscopy as ewll as the results of our attempts to carry out pleurodesis by talc were also studied. Pleural glucose levels were less than 60 mg/dl in 16 cases, and the cytologic yield was positive in 14 of these cases (87%). The glucose value rose above this level in 61 cases, and the cytology was positive in 30 cases (49%; p < 0.006). A pH less than 7.30 was encountered in 18 cases and there were positive cytologic findings in 14 of these cases (78%). The pH was above 7.30 in 46 cases, and cytologic studies were positive in 22 cases (48%; p < 0.03). There were ten cases in which both the glucose and pH levels were low, and the cytology was positive in 9 cases (90%), while there were 40 cases in which both the glucose and pH levels were high and cytologic yields of 20 of these cases were positive (50%; p < 0.03). The extnesion of the lesions observed during thoracoscopy showed important differences as far as this related to the glucose levels (p < 0.005), but this relationship as it concerned pH levels was even more significant (p < 0.0002). The differences were also highly significant (p < 0.003) when the glucose and pH were jointly considered. A significant statistical relationship was found between positive pleural cytological yields and the extension of the malignancies (p < 0.04). Attempts at pleurodesis were performed on 62 patients by spraying talc into the pleural cavity; 60 of these cases could be evaluated after a month. Good results were attained in 7 of 12 cases with low glucose (58%) and in 41 of 48 cases with normal glucose levels (85%) (nonsignificant difference). Pleurodesis was successful in 9 of 14 cases with low pH (64%) and in 33 of 36 cases with normal pH value (92%; p < 0.02). There were significant differences between mean values of glucose in cases with good and bad results of pleurodesis (108 versus 66 mg/dl, respectively; p < 0.03). There were even more striking differences found between mean values of pH (7.37 versus 7.17; p < 0.0001). We have reached the conclusion that in cases with both low pleural glucose and pH levels, there is a 90% probability that the cytologic yield of a neoplastic effusion will be positive (p < 0.03). As far as pleurodesis is concerned, we found that as pleural fluid glucose and pH values decrease, the outcome of pleurodesis is worse. One is able to predict that attempts at pleurodesis will fail in nearly half the cases (p < 0.02) if the pleural pH is less than 7.30. These findings are the consequence of the close relationship found between two pleural glucose and pH levels and the extension of lesions observed during thoracoscopy.