Biochemical features of urinothorax.

In three patients with obstructive uropathy and retroperitoneal urine collections, rapidly accumulating pleural effusions developed. The diagnosis of urinothorax was confirmed when chemical analysis of pleural fluid disclosed higher creatinine concentrations than found in simultaneously obtained serum samples. Similar determinations made in 71 specimens from control patients with pleural effusions showed that pleural creatinine concentration did not exceed the serum level in other conditions. We conclude that elevated pleural fluid creatinine level is specific for the diagnosis of urinothorax. Low pleural fluid glucose concentration may also be seen in these patients.