What is the sensitivity of pleural fluid cultures?

From the Guidelines

The sensitivity of pleural cultures is approximately 50%–60% at best, as demonstrated by large-scale studies 1. This means that conventional microbiological tests, such as culture of pleural fluid in plain tubes, fail to identify the causative organism in a significant proportion of patients. The yield of blood cultures is even lower, at less than 10% 1. Several factors contribute to the low sensitivity of pleural cultures, including the often low bacterial burden in pleural fluid and the fastidious nature of many organisms causing pleural infections. To improve the microbiological yield, inoculating pleural fluid into blood culture bottle media can be beneficial 1. Additionally, using image-guided parietal pleural biopsy for microbiological assessment can also increase the yield 1. It is essential to note that the volume of pleural fluid sent for microbiological examination can impact the sensitivity, with larger volumes (at least 25 mL) recommended whenever possible 1. In cases where the volume of fluid is limited, prioritizing the use of blood culture bottles over plain, sterile containers can help maximize the culture yield 1. Overall, the low sensitivity of pleural cultures highlights the need for empirical antibiotic therapy in many cases and the importance of using additional diagnostic techniques to guide treatment. Key points to consider when interpreting pleural cultures include:

• The potential for low bacterial burden in pleural fluid
• The presence of inhibitory substances in infected pleural fluid
• The fastidious nature of many organisms causing pleural infections
• The importance of using blood culture bottles to increase sensitivity
• The need for empirical antibiotic therapy in many cases due to the low sensitivity of pleural cultures.

From the Research

Sensitivity of Pleural Cultures

• The sensitivity of pleural cultures can vary depending on the type of culture and the specific condition being diagnosed.
• A study published in Chest in 2005 found that the positive yield of microbiologic smears and cultures on pleural fluid specimens is low, particularly in the outpatient setting and in patients with free-flowing effusions 2.
• The study reported that true pathogens were identified in only 19 of 1,320 pleural fluid cultures (1.4%) belonging to 15 patients (3.2% of those who had cultures performed on their pleural fluid specimen).
• Another study published in the Scandinavian journal of clinical and laboratory investigation in 2007 found that the sensitivities of pleural fluid culture and AFB smear were 42% and 1%, respectively, for the diagnosis of pleural tuberculosis 3.
• A study published in Respiratory medicine in 2006 found that microbiological studies were positive on the pleural fluid of 50 patients (19.3%) with parapneumonic pleural effusion, but the need for pleural drainage was correctly predicted by pleural fluid parameters in 48 of the 50 patients with positive microbiological results (96%) 4.
• A review published in Expert review of respiratory medicine in 2019 noted that the microbiology of pleural infection is unique compared to the lung, and highly variable, and that higher culture yields from pleural biopsy may add new insights into the etiopathogenesis 5.
• However, it's worth noting that the sensitivity of pleural fluid cytology for malignant pleural effusions was found to be 58.2% in a systematic review and meta-analysis published in Thorax in 2023, with substantial heterogeneity present among studies 6.