## Investigation of Choice in Bronchopneumonia **Key Point:** Sputum culture and Gram stain is the gold standard microbiological investigation for identifying the causative organism in bronchopneumonia and guiding targeted antibiotic therapy. ### Why Sputum Culture & Gram Stain? Bronchopneumonia typically presents with: - Patchy, multifocal infiltrates (peribronchial distribution) - Involvement of multiple lobes - Commonly caused by *Streptococcus pneumoniae*, *Haemophilus influenzae*, *Moraxella catarrhalis*, or gram-negative organisms in hospitalized/elderly patients **High-Yield:** Gram stain provides rapid morphological identification (gram-positive cocci in pairs = *S. pneumoniae*; gram-negative coccobacillus = *H. influenzae*), while culture confirms organism and allows antimicrobial susceptibility testing (AST). ### Role of Other Investigations | Investigation | Role in Pneumonia | Limitation | |---|---|---| | Sputum culture & Gram stain | **Organism identification + AST** | **Gold standard** | | Serum procalcitonin | Inflammatory marker; prognostic | Non-specific; does not identify organism | | Chest CT | Evaluates complications (abscess, empyema) | Not first-line for diagnosis; unnecessary in uncomplicated cases | | CBC with differential | Assesses WBC response; prognosis | Non-specific; does not identify pathogen | **Clinical Pearl:** In bronchopneumonia, a good-quality sputum sample (>25 WBC, <10 epithelial cells per low-power field) is essential to avoid contamination and guide empiric therapy until culture results return. **Tip:** Always obtain sputum culture BEFORE starting antibiotics in hospitalized or severely ill patients to maximize diagnostic yield.
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