Urinothorax and pleural fluid creatinine: a retrospective analysis of pleural fluid studies at a tertiary care center and a review of the literature.

BACKGROUND: Urinothorax is a somewhat vaguely defined entity in the pulmonary literature. It is believed to be due to obstructive renal failure resulting in translocation of urine into the pleural space, presenting as transudative pleural effusions. The literature is sparse, and much of the reported data revolves around case reports and series, with less than 100 cases reported to date. The hallmark finding defining urinothorax is a pleural fluid to serum creatinine ratio greater than 1, although this ratio has not been verified in the literature. Further, the utility of this ratio beyond identification of urinothorax is unknown. Pleural fluid creatinine values may be useful beyond identification of urinothorax, and may have diagnostic value in identifying pleural effusions from persistent volume overload, although further studies are needed to verify this. More likely however, there is a paucity of data in the current literature to support the use of pleural fluid creatinine routinely in the identification of urinothorax, as we have identified in this study. This study aims to elucidate the normal values of pleural fluid creatinine and its utility in pleural disease.

METHODS: Here we report a large retrospective study on pleural fluid analyses at a tertiary care center, correlating pleural fluid to serum creatinine ratios with the etiology of pleural effusion.

RESULTS: We present a retrospective study on the analysis of over 300 pleural fluid studies, with a focus on pleural fluid to serum creatinine ratio and its relation to pleural disease.

CONCLUSIONS: A pleural fluid to serum creatinien ratio of 1:1 is not specific for the diagnosis of urinothorax given its nearly universal distribution amongst pleural effusions of all etiologies. Further studies are needed to establish normal values of pleural fluid creatinine and specifically its utility in true urinothorax and challenging cases such as pseudoexudates.