Pearls and myths in pleural fluid analysis

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.

Predictive factors, microbiology and outcome of patients with parapneumonic effusion

“…Subsequently, the biochemical and microbiological analyses of the pleural fluid and its macroscopic appearance provide criteria for the classification of patients with pleural effusion into two new subgroups: patients with uncomplicated parapneumonic effusion (UPE) and patients with empyema/ complicated parapneumonic effusion (E/CPE) [1].…”

Handling Pleural Fluid Samples for Routine Analyses

“…While the volume of pleural fluid necessary for the maximum yield of cytological analysis is controversial, some guidelines suggest submitting at least 20 mL (11). The larger the sediment to be obtained in order to maximise the yield of cell blocks, the greater the volume of fluid that needs to be centrifuged.…”

Diagnosis of pleural infection: state-of-the-art

“…However, a pleural fluid dominated by polymorphonuclear leukocytes can also occur in 10% and 20% of tuberculous and malignant effusions, respectively, as well as in a number of acute effusions [21]. Recently, Porcel et al examined the diagnostic usefulness of pleural fluid routine biochemistries (white blood cell count and differential, pH, glucose, lactate dehydrogenase [LDH], adenosine deaminase [ADA]) and C-reactive protein (CRP) for labeling parapneumonic effusions among nearly 2,000 non-purulent exudates [22].…”