TABLE 1.

Role of PCT levels in the interpretation of clinical microbiology data in patients with lower respiratory tract infections

Bacterial pathogen detected	Viral pathogen detected	Procalcitonin level (ng/ml)	Interpretation
No	No	≤0.05	No evidence of bacterial or viral infection
No	No	0.5-1,000	Innate immunity activated; suspect noncultured bacteria, e.g., oral anaerobic organisms
No	Yes	≤0.05	Viral infection
No	Yes	0.25-1,000	Dual viral and bacterial infection; failure to identify etiologic bacteria
Yes	Yes	0.25-1,000	Dual infection with virus and bacteria
Yes	No	≤0.05	Bacterial colonization
Yes	Yes	≤0.05	Bacterial colonization and viral infection