Clinical meaning
Pneumonia diagnosis combines clinical presentation (cough, fever, dyspnea, pleuritic pain) with radiographic confirmation (new infiltrate on CXR). The clinician must differentiate community-acquired (CAP), hospital-acquired (HAP >= 48h after admission), and aspiration pneumonia. Severity assessment using validated tools guides site-of-care decisions. CRB-65 (Confusion, Respiratory rate >= 30, Blood pressure systolic < 90 or diastolic <= 60, age >= 65): score 0 = outpatient, 1-2 = consider admission, 3-4 = urgent hospitalization. The Pneumonia Severity Index (PSI/PORT) uses demographics, comorbidities, vital signs, and labs to stratify into classes I-V. Biomarkers aid diagnosis: procalcitonin > 0.25 mcg/L supports bacterial etiology, CRP > 100 mg/L with fever and consolidation has 96% specificity for bacterial pneumonia. Blood cultures are recommended for all hospitalized patients before antibiotic administration.