Zinc, copper, and iron were measured in the pleural fluid of 86 patients with benign conditions (including congestive heart failure, pulmonary embolus, collagen disease, pneumonitis, non-specific pleuritis, and tuberculosis) and in 116 patients with malignant disease (including lymphoma, breast carcinoma, primary lung cancer, and metastatic lung cancer). Though a positive correlation was found between zinc and copper in the benign group and not in the malignant group, the test was not specific enough to differentiate benign from malignant disease, because of the wide scatter of results.A positive regression for serum copper on pleural fluid copper was found in the benign, lymphoma, and malignant groups, but the differences between these three were not sufficient to help in the differential diagnosis.These findings suggest that pleural fluid heavy metals do not have the specificity that has been reported for serum heavy metals in benign and malignant disease and in malignant lymphoma.
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