Pleural fluid biochemistry: A first step toward an etiological diagnosis of pleural effusions

Abstract

The analysis of pleural fluid (PF) is the most important diagnostic element in identifying the cause of pleural effusions. PF biochemistries, in particular, are available immediately and offer relevant clinical information. The measurement of proteins and lactate dehydrogenase (LDH) in PF and blood (Light's criteria) establishes the transudative or exudative nature of effusions. Transudates are commonly caused by heart failure (HF), but diuretic therapy may concentrate PF causing higher levels of protein and/or LDH and, therefore, leading to a misclassification as an exudate. In this scenario, a serum-PF albumin gradient > 1.2 g/dL points to a true transudate. Furthermore, elevated concentrations of the natriuretic peptide N-terminal pro-brain natriuretic peptide are virtually pathognomonic of HF as the primary or, at least, secondary diagnosis. In exudates with predominantly polymorphonuclear leukocytes (> 50%), a bacterial infection of the pleural space should be considered, particularly if PF C-reactive protein levels are high. A pleural pH < 7.15 or a glucose < 40 mg/dL in a parapneumonic effusion indicates the need for a drainage tube. When lymphocytes predominate in an exudate, cancer and tuberculosis are the two main diagnoses to consider; an adenosine deaminase activity > 35 U/L strongly supports the diagnosis of tuberculosis. Measuring tumor markers (e.g., carcinoembryonic antigen, CA15-3) under the premise of using 100% specific cutoff points can increase the diagnostic yield for malignancy.

Estimation of Serum Adenosine Deaminase-2 (ADA2) as One of the Non- Invasive Diagnostic Marker of Pleural Effusion in Systemic Lupus Erythromatosus

“…As well, Porcel JM et al ( 2021) 23 noted that level of ADA level in pleural fluid increased in patients with pleural effusion, but no confirmation of pleural effusion was seen on ANA profile, which is a costly test. We do not have access to ANA profiles on the spot in our remote areas, so evaluating serum ADA2 gives strong suspicion regarding the development of pleural effusions in SLE patients.…”