Serum procalcitonin (PCT) has become a routinely utilized parameter with a high prediction value of the severity of bacterial infectious complications and their immediate outcomes. Whereas the utility of PCT in differentiating between bacterial and viral infection is generally accepted, its significance in fungal infections has yet to be determined. The aim of the study was to determine the role of PCT testing in patients at high risk for invasive fungal infections.

Immunocompromised hematological patients undergoing cyclic chemotherapy treatment or allogeneic hemopoietic stem cell transplantation with infectious complications in which the infectious agents were identified during the disease course were evaluated. In patients with bacterial infection, positive hemocultures were documented, and in patients with fungal infection, the presence of either proven or probable disease was confirmed according to Ascioglu criteria. C-reactive protein (CRP) and PCT were prospectively assessed from the day following fever onset, for four consecutive days.

Overall, 34 patients were evaluated, 21 with bacterial and 13 with fungal infections. Significant elevations of CRP concentrations (i.e., above the upper normal limit) were observed in all patients, with a tendency toward higher levels in bacterial (both gram-positive [Gr+] and Gr-negative [Gr−]) than in fungal infections. PCT levels were significantly elevated in patients with bacterial infections (e.g., predominantly in Gr− compared to Gr+), whereas in patients with fungal infections, we identified minimal or no PCT elevations, p < 0.01. For the fungal infections, according to constructed receiver operating characteristic curves, a combination of PCT <0.5 μg/L and CRP 100–300 mg/L offers the best specificity, sensitivity and positive and negative predictive values (81, 85, 73, and 89 %, respectively).

Altogether, our data suggest that the finding of substantially elevated CRP combined with low PCT in immunocompromised patients may indicate systemic fungal infection. The use of this combination might simplify the diagnostic process, which otherwise can often be lengthy and arduous.