Biomarkers improve mortality prediction by prognostic scales in community-acquired pneumonia.

Background: Prognostic scales provide a useful tool to predict mortality in community-acquired pneumonia (CAP). However, the inflammatory response of the host, crucial in resolution and outcome, is not included in the prognostic scales.

Methods: We aimed to investigate whether information about the initial inflammatory cytokine profile and markers increases the accuracy of prognostic scales to predict 30-days mortality. To this aim a prospective cohort study in two tertiary care hospitals was designed. Procalcitonin (PCT), C-reactive protein (CRP), and the systemic cytokines tumor necrosis factorα(TNFα), interleukines IL-6, IL-8 and IL-10 were measured at admission. Initial severity was assessed by PSI (pneumonia severity index), CURB-65 and CRB-65 scales. 453 hospitalized CAP patients were included.

Results: The 36 patients who died (7.8 %) had significantly increased levels of IL-6, IL-8, PCT and CRP. In regression logistic analyses, high levels of CRP and IL-6 showed independent predictive value for predicting 30-days mortality, after adjustment for prognostic scales. Adding CRP to PSI significantly increased the area under the ROC curve (AUC) from 0.80 to 0.85, that of CURB-65 from 0.82 to 0.85 and that of CRB65 from 0.79 to 0.85. Adding IL-6 or PCT values to CRP did not significantly increase AUC of any scale. When using simultaneously both scales and CRP the AUC was 0.88.

Conclusions: Adding CRP levels to PSI, CURB-65 and CRB-65 scales improves the 30-days mortality prediction. The highest predictive value is reached with a combination of both scales and CRP. Further validation of that improvement is needed