[A 30-year-old man with a puddle of pleural effusion].

Background: The pleural effusion found in urinothorax is traditionally classified as transudate. In some cases, however, the Light-criteria can show an exudate.

Case Description: We describe the case of a 30-year-old man who attended the emergency department with shortness of breath and severe, diffuse, chest pain; this occurred two days after he had undergone a left-sided percutaneous nephrolithotomy by a urologist. A chest X-ray showed pleural effusion in the left basal region. Based on the Light-criteria, this effusion was an exudate. We made the diagnosis of urinothorax following percutaneous nephrolithotomy.

Conclusion: When urinothorax is suspected, biochemical analysis can reveal either a transudate or an exudate. The pleural fluid/serum creatinine ratio can be a valuable addition to the Light-criteria in this setting. The Light-criteria should always be interpreted in a clinical context.