Page "Pleural effusion" Paragraph 29

The traditional definitions of transudate as a pleural effusion due to systemic factors and an exudate as a pleural effusion due to local factors have been used since 1940 or earlier ( Light et al., 1972 ).

Previous to Light's landmark study, which was based on work by Chandrasekhar, investigators unsuccessfully attempted to use other criteria, such as specific gravity, pH, and protein content of the fluid, to differentiate between transudates and exudates.

Light's criteria are highly statistically sensitive for exudates ( although not very statistically specific ).

More recent studies have examined other characteristics of pleural fluid that may help to determine whether the process producing the effusion is local ( exudate ) or systemic ( transudate ).

The chart to the right, illustrates some of the results of these more recent studies.

However, it should be borne in mind that Light's criteria are still the most widely used criteria.