A comparative evaluation of salivary and serum procalcitonin to identify infants with serious bacterial infections.

Differentiating serious bacterial infections (SBIs) from viral illnesses in infants remains challenging. Although serum procalcitonin (PCT) is a well-established biomarker, its measurement requires invasive blood sampling. This study investigated the correlation between salivary and serum PCT and evaluated the diagnostic accuracy of salivary PCT for identifying SBIs in infants under 1 year of age. This prospective observational study included 160 infants under one 1 year of age presenting to a pediatric emergency department with suspected SBI. Paired serum and saliva samples were collected. Salivary PCT and serum PCT levels were measured. Serum C-reactive protein (CRP), a routinely used inflammatory marker in pediatric emergency practice, was included as a comparator biomarker. Patients were classified into SBI and viral infection groups based on final diagnoses. The diagnostic accuracy of the biomarkers was assessed and compared using receiver operating characteristic (ROC) curve analysis.Of the 160 infants (median age 8 months; 63% male), 11.3% (n = 18) were diagnosed with SBI and 88.7% (n = 142) with viral infections. Median salivary PCT levels were markedly higher in the SBI group than in the viral infection group (69.3 pg/mL vs. <0.01 pg/mL; p < 0.001). The area under the curve (AUC) for diagnosing SBI was 0.92 for salivary PCT, 0.96 for serum PCT, and 0.88 for serum CRP. At a cutoff value of 31.3 pg/mL, salivary PCT demonstrated a sensitivity of 89% and a specificity of 92.3%, with a negative predictive value (NPV) of 98.7%. A weak but statistically significant correlation was found between serum and salivary PCT levels (r = 0.250; p = 0.001). Conclusion: Salivary PCT shows strong correlation with serum PCT and demonstrates high diagnostic accuracy as a non-invasive biomarker for identifying SBIs in infants. Its performance approaches that of serum PCT and exceeds that of serum CRP, highlighting its potential clinical value in reducing the need for invasive blood sampling. What is Known: • Serum procalcitonin (PCT) is a well-established marker for detecting serious bacterial infections (SBI) in infants, surpassing CRP, though it requires invasive sampling. What is New: • Salivary PCT demonstrates comparable diagnostic performance to serum PCT and exceeds CRP, highlighting its potential as a non-invasive alternative for SBI assessment in infants.