Pearls and myths in pleural fluid analysis

Our plain-English summary of Pearls and myths in pleural fluid analysis, by J.M. Porcel (Respirology, 2011).

The study

• Author: J.M. Porcel
• Journal: Respirology
• Published: 2011;16(1):44-52
• Type of article: Review
• Cited by: 78 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Virtually all patients with a newly discovered pleural effusion should undergo thoracentesis to aid in diagnosis and management. The routine pleural fluid (PF) evaluation usually includes the following: cell count and differential; tests for protein, LDH, glucose, adenosine deaminase, cytology and, if infection is a concern, pH and bacterial and mycobacterial cultures. Distinguishing transudates from exudates with Light's criteria is a pragmatic first step. If the effusion is an exudate, various PF tests have proven diagnostic utility: adenosine deaminase levels >35 IU/L usually indicate tuberculosis in lymphocyte-predominant PF; pH < 7.2 or glucose less than 60 mg/dL allow the clinician to identify complicated parapneumonic effusions; and conventional cytology may reveal malignant cells in 60% of the patients with malignant effusions. A number of optional PF tests may complement the diagnostic approach to an undiagnosed pleural effusion. For example, natriuretic peptide assays significantly improve the accuracy of a diagnosis of cardiac pleural effusion, whereas PF mesothelin levels greater than 20 nmol/L are highly suggestive of mesothelioma.

© 2010 The Author. Journal compilation © 2010 Asian Pacific Society of Respirology.

In plain English

This is a narrative review by a single author in an invited series on pleural disease. It reported no new study of asbestos-exposed people and did not discuss asbestos. It set out common beliefs ("myths") and practical points ("pearls") about testing the fluid that collects around the lung (pleural effusion). Among the published studies it described, one measured pleural fluid mesothelin in 24 patients with mesothelioma, 67 with pleural metastases and 75 with benign conditions. In that study, levels above 20 nmol/L diagnosed mesothelioma more often than cytology did (71% vs 35%). A cited thoracoscopic series of 556 malignant effusions found that fluid cytology detected 41% of mesotheliomas. Another cited study reported 20% for the sarcomatoid type. In unpublished data from the author's own database, Light's criteria separated exudates from transudates with 95% overall accuracy. The author concluded that pleural fluid mesothelin above 20 nmol/L is highly suggestive of mesothelioma. The author also concluded that a negative cytology result does not rule out malignancy.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Narrative review (invited review, single author), summarising published studies and some unpublished data from the author's own database
• Who was studied: Published studies of patients with pleural effusion, plus unpublished data from the author's pleural database (Lleida, Spain). The review focuses on tests available in most clinical laboratories.
• Exposure: Not an exposure study, and asbestos is not mentioned. The subject is diagnostic tests on pleural fluid: cell count and differential, protein, LDH, glucose, pH, adenosine deaminase, cytology, cultures, tumour markers, mesothelin and others.
• Main results:
  • In a cited study (Davies et al.) of 24 patients with mesothelioma, 67 with pleural metastases and 75 with benign pleural conditions, pleural fluid mesothelin above 20 nmol/L detected mesothelioma with a positive likelihood ratio of 7.1 and a negative likelihood ratio of 0.32.
  • In the same cited study, mesothelin measurement diagnosed mesothelioma more often than cytological examination (71% vs 35%).
  • In a cited thoracoscopic series of 556 malignant pleural effusions, overall cytology sensitivity was 60%. It was 41% for mesothelioma and 18% for lymphoma.
  • Another cited study reported that, among mesothelioma patients, cytology sensitivity was lowest for the sarcomatoid histological type (20%).
  • The author stated that a false-negative rate of about 40% has been reported for pleural fluid cytology.
  • In unpublished data from the author's database (2115 effusions), Light's criteria identified exudates with an overall diagnostic accuracy of 95%. Sensitivity was 97.5% and specificity 73.8%.
  • In the author's unpublished study of 603 patients with malignant pleural effusions, cytology sensitivity was 50% (95% CI: 46–54%) for the first specimen. It was 57% for the second and 58.2% for the third separate specimen.
• The authors' conclusion: The author concluded that pleural fluid mesothelin levels greater than 20 nmol/L are highly suggestive of mesothelioma. The author also concluded that a negative pleural fluid cytology result does not rule out malignancy.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Pleural Effusion, Thoracentesis, Cytology, Exudate, Light's Criteria, Mesothelin, Mesothelioma.

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