Comparative Evaluation of Sputum and Bronchoalveolar Lavage (BAL) Cultures in Clinically Suspected Cases of Community-Acquired Lower Respiratory Tract Infections

TL;DR

The study compares sputum and bronchoalveolar lavage (BAL) cultures for diagnosing pneumonia, finding that sputum is reliable for most cases while BAL is better for complex or unclear cases.

Contribution

The study provides a comparative diagnostic evaluation of sputum and BAL cultures in lower respiratory tract infections, emphasizing their relative strengths.

Findings

Sputum culture has high specificity (100%) and 78.2% sensitivity compared to BAL.

BAL cultures show superior sensitivity and higher pathogen yield than sputum.

Pseudomonas aeruginosa was the most common isolate in both sample types.

Abstract

Objectives: This study aimed to compare diagnostic agreement between culture results from bronchoalveolar lavage (BAL) and sputum samples for common pneumonia-causing pathogens and to evaluate the value of less invasive alternative diagnostic methods for pneumonia.

Materials and methods: This retrospective study was conducted at a tertiary care hospital in North India from January 2022 to December 2022. Samples were inoculated directly onto blood agar, chocolate agar, and MacConkey agar. Confirmation of isolates and antimicrobial susceptibility testing was performed using an automated system (VITEK 2, bioMérieux, Marcy-l’Étoile, France). A total of 253 paired BAL and sputum samples collected in close succession were analyzed for concordance. Statistical analyses were performed using SPSS Statistics version 28 (IBM Corp. Released 2021. IBM SPSS Statistics for Windows, Version 28.0. Armonk, NY: IBM Corp.). The intraclass correlation coefficient (ICC) was used to assess the level of agreement between the two methods.

Results: Among 253 patients, 171 (67.6%) were male, with a mean age of 56.7 ± 2.1 years. Significant bacterial growth was observed in 43 (16.9%) sputum and 55 (21.7%) BAL specimens. Pseudomonas aeruginosa was the most common isolate in both sample types. Overall concordance between sputum and BAL cultures was 80.2%, with near-perfect agreement for P. aeruginosa (ICC = 0.90). The sensitivity and specificity of sputum culture were 78.2% and 100%, respectively, compared with BAL.

Conclusions: Sputum culture serves as a reliable first-line diagnostic tool with high specificity, whereas BAL demonstrates superior sensitivity and pathogen yield. BAL should be considered in cases with negative or inconclusive sputum results to enhance diagnostic accuracy in lower respiratory tract infections.

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