Sequential thoracentesis: minor change of zinc compared to other selected essential trace elements in the serum.

This study first indicates that the serum trace element Zn tends to decrease in the course of sequential thoracenteses. Other selected essential elements such as copper (Cu), manganese (Mn), molybdenum (Mo), and cobalt (Co) do not reveal loss changes in their serum levels. Therefore, Zn should be monitored in patients who undergo repeated thoracentesis. To measure the magnitude of changes in serum trace elements and the clinical relevance of potential imbalances, concentrations of the essential elements are analyzed in 57 serum/effusion pairs obtained from 5 patients (4 male, 1 female; age 28-78 yr) who underwent repeated thoracenteses as a result of recurrent pleural effusion. All patients declined other therapeutic options such as chemical pleurodesis and/or chest tube placement. The total volumes of fluid removed ranged from 2.3 to 19.3 L and the frequency of thoracentesis ranged from 6 to 15 within a period of 102-174 days. Two patients had benign pleural disease and three had malignancies. Three patients suffered from pleural effusions resulting from exudates (total protein content > 3.0 g/dL, LDH > 200 U/L), and two resulting from transudates (total protein < 3.0 g/dL, LDH < 200 U/L). All trace elements were simultaneously determined by inductively coupled argon plasma-mass spectrometry. In addition, the concentrations of the following clinically relevant parameters were analyzed by standard methods: total protein, pH, leukocyte count, lactate dehydrogenase, and glucose.