A Blood Test to Differentiate Bacterial From Viral Lower Respiratory Infections—Procalcitonin

Abstract & Commentary

Synopsis: The use of serum procalcitonin helps to differentiate bacterial from viral lower respiratory infections and may reduce the use of unnecessary antibiotics.

Source: Christ-Crain M, et al. Lancet. 2004;363:600-607.

This randomized, controlled trial from Switzerland looked at 243 patients admitted with suspected lower respiratory infection. Half of the patients received standard diagnosis and therapy while the other half was able to use a serum procalcitonin level to help guide therapy. An elevated level (0.5 mg/L or higher) suggests bacterial infection while a low level (less than 0.25 mg/L) suggests viral infection. The final diagnoses in both groups was pneumonia in 36% of patients, exacerbation of COPD in 25%, acute bronchitis in 24% and an exacerbation of asthma in 5%. In the standard group, 83% received antibiotics while in the procalcitonin group, only 44% received them. Antibiotic use was reduced in all diagnostic subgroups. There was no difference in outcome between the 2 groups.

Comment By Joseph E. Scherger, MD, MPH

So often we are frustrated not knowing whether a respiratory infection is bacterial or viral. The overlap in signs and symptoms is too great to rely on the clinical picture, especially when the patient is quite sick. How nice it would be to have a reliable serum marker for bacterial vs viral infection. Procalcitonin, a precursor of calcitonin may turn out to be such a marker.

Dr. Scherger, Clinical Professor, University of California, San Diego, is Associate Editor of Internal Medicine Alert.