Fever suggests the presence of microbial infection in critically ill patients. The aim was to compare the role of old and new biomarkers in predicting absence or presence of microbial infection, its invasiveness and severity in critically ill patients with new onset fever.

We prospectively studied 101 patients in the intensive care unit with new onset fever (>38.3 °C). Routine infection parameters, lactate, procalcitonin (PCT), midregional pro-adrenomedullin (MR proADM), midregional pro-atrial natriuretic peptide (MR proANP) and copeptin (COP) were measured daily for three days after inclusion. Likelihood, invasiveness (by bloodstream infection, BSI) and severity of microbial infection were assessed by cultures, imaging techniques and clinical courses.

All patients had systemic inflammatory response syndrome; 45% had a probable or proven local infection and 12% a BSI, with 20 and 33% mortality in the ICU, respectively. Only peak PCT (cutoff 0.65 ng/mL at minimum) was of predictive value for all endpoints studied, i.e. BSI, septic shock and mortality (high risk infection) and infection without BSI, shock and mortality (low risk infection), at areas under the receiver operating characteristic curves varying between 0.67 (P = 0.003) and 0.72 (P < 0.001). In multivariable analysis, the combination of C-reactive protein and lactate best predicted high risk infection, followed by PCT. For low risk infection, PCT was the single best predictor.

In critically ill patients with new onset fever, plasma PCT as a single variable, among old and new biomarkers, best helps, to some extent, to predict ICU-acquired, high risk microbial infection when peaking above 0.65 ng/mL and low risk infection when peaking below 0.65 ng/mL.