C-reactive protein and procalcitonin levels, white blood cell count, and erythrocyte sedimentation rate have limited use in the diagnosis of bacterial pneumonia.22 One older study of children younger than 16 years showed that 93 percent of those with a white blood cell count greater than 20,000 cells per mm3 (20 × 109 per L) improved with antibiotic therapy, compared with only 50 percent of those with a count of less than 10,000 cells per mm3 (10 × 109 per L).23 The improvement with antibiotics was significant in patients with a white blood cell count greater than 15,000 cells per mm3 (15 × 109 per L), which suggests an association with bacterial pneumonia. Sputum cultures are difficult to obtain and are of limited use in diagnosis or therapy. Blood culture results have not been shown to change clinical management and often do not yield a pathogen.24