PCT Effective to ID Invasive Bacterial Infection in Febrile Infants

A procalcitonin (PCT) assay has better diagnostic accuracy than C-reactive protein (CRP) concentration, white blood cell (WBC) count, and absolute neutrophil cell (ANC) measurement for detecting invasive bacterial infections (IBIs) in febrile infants less than 3 months of age, according to a study published in the January issue of JAMA Pediatrics. Both PCT and CRP perform similarly for identifying severe bacterial infections (SBIs) in these infants, although urinalyses may be adequate to detect urinary tract infections (UTIs), which account for the majority of these SBIs.

"Although it would be unwise to use the PCT assay alone, combined with careful analysis of the case history, physical examination, and appropriate tests, it provides important information for the detection of IBIs in this population," writes lead author Karen Milcent, M.D., from Paris-Saclay University in France.

Given that there are few diagnostically reliable symptoms or clinical signs and these signs are often indistinguishable from viral infection in young infants, a complete sepsis evaluation, empirical antibiotic therapy, and hospital admission are recommended for febrile infants up to one month of age and are common for those between one and two months of age, the authors say. Evaluation of PCT assays have been lacking in infants less than 3 months.

The French researchers prospectively evaluated infants aged 7 to 91 days (n= 2,047) consecutively admitted for fever to 15 French pediatric emergency departments (Oct. 1, 2008 through March 31, 2011). The researchers found that 6.8 percent of infants were diagnosed with SBIs, while one percent had IBIs. Blood cultures identified 11.0 percent and 1.7 percent of those infections, respectively. The most common SBIs were UTIs (115 of 139). Of the IBIs, there were 13 cases of bacteremia and eight cases of bacterial meningitis.

The PCT assay offered an area under the curve (AUC) similar to that for CRP concentration for the detection of SBI (0.81 versus 0.80, respectively). However, the AUC for the detection of IBI for the PCT assay was significantly higher than that for the CRP concentration (AUC, 0.91 versus 0.77, respectively). Using a cutoff value of 0.3 ng/mL for PCT and 20 mg/L for CRP, negative likelihood ratios were 0.3 for identification of SBI and 0.1 and 0.3 for identifying IBI, respectively. Similar results were seen for infants younger than one month of age and for those with recent fever onset (less than 6 hours).

"Our results suggest that it may be possible to improve clinical practice for the treatment of young febrile infants," write the authors "Although our optimal PCT threshold is calculated in isolation and may be different in the multivariable model, one advantage of our results may be the potential to avoid lumbar puncture, particularly in patients older than 1 month with a PCT level less than 0.3 ng/mL."

Takeaway: This study provides evidence that PCT assays have better diagnostic accuracy than CRP for detecting IBI in very young febrile infants.