Commentary on the British Thoracic Society guidelines for the investigation of unilateral pleural effusion in adults.

The publication of guidelines for the investigation of unilateral pleural effusion in adults by the British Thoracic Society has focused attention on this subject which, although comprising only a small proportion of laboratory workload, is a fairly common clinical problem. We critically reviewed the guidance applicable to clinical biochemistry laboratories and found a number of deficiencies. In particular, the need for anaerobic sample collection for pH measurement and preservation of samples for glucose assay is not mentioned and health and safety issues related to the handling of potentially infected fluids are also not considered. There are discrepancies between recommendations in the text and in the accompanying diagnostic algorithm, which require clarification. Measurement of total protein is an essential first step in the analysis of pleural fluid and will usually distinguish transudates from exudates. Measurement of lactate dehydrogenase activity is only required when total protein results are equivocal. There are practical difficulties with measurement of fluid pH as recommended in the guidelines and there is little evidence that such measurements are valuable. Similarly, there is little evidence to support the recommendation for measurement of complement in suspected rheumatoid effusions, and the recommendation for amylase isoenzyme studies if acute pancreatitis is a possibility is not practical. The different nature of pleural fluid demands a good understanding of the handling of these samples, the limitations of the analytical methods and the subsequent result interpretation by laboratory staff. We propose a modified diagnostic algorithm reflecting our criticisms of the original. Dialogue between the laboratory and local clinicians, possibly with the production of local guidelines, informed by these recommendations, should help optimize diagnostic management of patients with pleural effusion.