Which measurement BEST predicts disease severity in RSV infection?

• A. CXR
• B. WBC count
• C. Blood pH
• D. Pulse Ox

Answer: (D)

Oxygenation status measured by pulse oximetry best predicts severity of RSV infection. In infants and young children with bronchiolitis, the main danger is hypoxemia from airway inflammation and obstruction. Pulse oximetry provides a real-time, noninvasive readout of how well the lungs are exchanging oxygen, which directly reflects how severely the disease is affecting gas exchange and helps guide need for supplemental oxygen or hospital care.

Chest X-ray findings can vary and do not consistently track illness severity—some with significant symptoms may have minimal radiographic abnormalities, while others with obvious X-ray changes may be clinically mild. White blood cell count is a nonspecific marker of infection and does not indicate the degree of respiratory compromise. Blood pH indicates acid-base status but shifts late in the course and does not reliably predict current severity or need for intervention in RSV bronchiolitis.