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Diagnostic evaluation of a pleural effusion in adults: Initial testing

John E Heffner, MD
Section Editor
V Courtney Broaddus, MD
Deputy Editor
Geraldine Finlay, MD


Determining the cause of a pleural effusion is greatly facilitated by analysis of the pleural fluid. Thoracentesis is a simple bedside procedure with imaging guidance that permits fluid to be rapidly sampled, visualized, examined microscopically, and quantified for chemical and cellular content. A systematic approach to analysis of the fluid in conjunction with the clinical presentation allows clinicians to diagnose the cause of an effusion, narrow the differential diagnoses, and design a management plan in a majority of patients who undergo pleural fluid analysis.

An approach to pleural fluid analysis will be presented here. Pleural fluid microbiologic tests, pleural imaging, the technique of thoracentesis, and an approach to pleural effusions of uncertain etiology after the initial evaluation are discussed separately. (See "Imaging of pleural effusions in adults" and "Diagnostic thoracentesis" and "Diagnostic evaluation of pleural effusion in adults: Additional tests for undetermined etiology" and "Tuberculous pleural effusion" and "Pleural effusions in HIV-infected patients" and "Parapneumonic effusion and empyema in adults".)


The indication for diagnostic thoracentesis is the new finding of a pleural effusion. Observation, in lieu of diagnostic thoracentesis, may be warranted in uncomplicated heart failure and viral pleurisy. In the former setting, the clinical diagnosis is usually secure; in the latter, there is typically a small amount of fluid. However, if the clinical situation is atypical or does not progress as anticipated, thoracentesis should be performed. The indications and contraindications of thoracentesis are presented separately. (See "Diagnostic thoracentesis".)


Only a select number of diagnoses can be established definitively by thoracentesis. These include effusions as a result of malignancy, empyema, tuberculous pleurisy, fungal infection of the pleural space, chylothorax, cholesterol effusion, urinothorax, esophageal rupture, hemothorax, peritoneal dialysis, and extravascular migration of a central venous catheter (table 1) [1]. Rarer conditions that can be diagnosed by thoracentesis include glycinothorax, cerebrospinal fluid leakage, and parasitic infection of the pleural space [1].

Positive pleural fluid lupus erythematosus (LE) cell preparation tests, pleural fluid antinuclear antibodies (ANA) titers ≥1:160, and a pleural fluid to serum ANA ratio ≥1 had previously been considered diagnostic of lupus pleuritis. However, none of these findings occurs solely in lupus pleuritis. Most clinical laboratories no longer perform lupus cell preparation tests, which are lengthy and complex [2-4]. Although LE cells may be incidentally detected by pleural fluid cytology, this finding has low diagnostic utility. This is because LE cells have been identified in routine pleural fluid cytologic examinations in non-lupus related effusions (eg, malignancy, rheumatoid arthritis) [2,5,6]. Similarly, small case series suggest that pleural fluid ANA titer ≥1:160 is not diagnostic of lupus pleuritis (specificity of 83 percent) [7] because such titers can also be found in exudative, parapneumonic, and malignancy-associated effusions [7-10]. Even an extremely high pleural fluid ANA >1:640 can occur in malignant effusions [10]. A pleural fluid ANA titer ≥1:160, however, remains a sensitive (86 to 100 percent) tool for detecting lupus pleuritis in patients with a known diagnosis of lupus [7-11] thereby differentiating between lupus pleuritis and other causes of pleural effusions in lupus patients. Using the ratio of pleural effusion to serum ANA of ≥1 further reduces the sensitivity and the specificity to 75 and 78, respectively [7,9,10]. The ANA staining pattern in pleural fluid does not provide any diagnostic value for lupus pleuritis [8,10]. Thus, measuring ANA titers has better negative predictive value than positive predictive value and appears to be useful only for excluding the diagnosis of lupus pleuritis, particularly in patients who have a known diagnosis of SLE. (See "Pulmonary manifestations of systemic lupus erythematosus in adults".)

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Literature review current through: Nov 2017. | This topic last updated: Nov 02, 2017.
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