During the 6-mo study period, 320 patients were admitted to our ICU. One hundred and nineteen patients were included in this study; 98 (82.3%) of these were still in the ICU on day 3. Among the 21 other patients, 12 died and nine were discharged alive before day 3. Patient characteristics are reported in Tables and . The reason for immunodepression was a hematological malignancy in 64 patients (53.8%), a solid tumor in 26 patients (21.8%), HIV infection in 31 patients (26%, including AIDS in 19 patients [16%]), and use of immunosuppressive agents in ten patients (8.4%). Of the included patients, 27 had neutropenia at ICU admission (22.7%) and eight were stem cell-transplant recipients (6.7%; allogeneic SCT in four patients).
The physicians suspected bacterial sepsis at ICU admission in 81 (68.1%) patients (Figure ). Antimicrobials were started before ICU admission in 37 (31.1%) patients, and they were administered on the first ICU day to 82 (69%) patients.
The final diagnosis was clinically documented bacterial sepsis in 34 (28.6%) patients and microbiologically documented bacterial sepsis in 24 (20.2%) patients; thus, 58 (48.7%) patients had bacterial infections. Of the remaining patients, 61 patients had no bacterial infection, including nine patients with nonbacterial infections (7.6%) and noninfectious conditions in 52 (43.7%) patients. Of the patients with microbiologically documented bacterial infections, 20 (83.3%) had positive blood cultures (Table ). Diagnoses in patients with noninfectious conditions were mainly malignant organ infiltration in 15 patients (28.9% of patients with noninfectious conditions), noninfectious neurological involvement in 11 patients (21.1% of patients with noninfectious conditions), cardiovascular events (including pulmonary embolism and cardiogenic pulmonary edema) in nine patients (17.3% of patients with noninfectious conditions), metabolic complications in nine patients (acute kidney injury or tumor lysis syndrome; 17.3% of patients with noninfectious conditions), and other noninfectious life threatening events in eight patients (15.4% of patients with noninfectious conditions).
Serum PCT concentrations on days 1 and 3 were significantly higher in patients with bacterial infections compared to all other patients (P < 0.0001; Figure , panel A). Patients with septic shock had higher serum PCT concentrations than patients who had severe sepsis without shock (15.18 ng/ml [4.17-48.81] vs 2.00 ng/ml [0.89-7.65]; P < 0.0001).
Procalcitonin levels (ng/ml) in patients with bacterial infection and in the other patients on Day 1 and Day 3 (panel A) and in survivors and nonsurvivors (panel B).
ROC curves are reported in Figure . The area under the curve (AUC) was 0.851 (95%CI 0.782-0.919). A cutoff value of 0.5 ng/ml was associated with 100% sensitivity but only 63% specificity. The performance of PCT at various cut-offs is reported in Table . In a multivariate analysis where bacterial infection was the outcome variable of interest, PCT concentrations of > 0.5 ng/ml independently predicted bacterial sepsis (Table ).
ROC curve analysis of the performance of procalcitonin for diagnosing bacterial infection on the first day in the ICU.
Performance of procalcitonin for detecting patients with bacterial infection at various cutoff values (± 95%CI)
Multivariate analysis identifying independent predictors for bacterial infection
All of the 58 patients with clinically or microbiologically documented bacterial infections had PCT values above 0.5 ng/ml and all received antimicrobial agents. Among the 24 patients admitted with suspected bacterial infections but in whom bacterial infection was secondarily ruled out, 15 (62%) had PCT values < 0.5 ng/ml and all but one received antimicrobial agents. Including PCT in an algorithm for antimicrobial agent use with a sensitivity threshold of 0.5 ng/ml would have avoided antimicrobial therapy in 15 patients on day 1. Of the nine patients with nonbacterial infections, one patient had viral infection (PCT 4.3), five patients had fungal infections (median [IQR] PCT = 0.37, range 0.17-32.3) and three had parasitic infections (median PCT = 0.37, range 0.11-4.6). Multivariate analysis identifying independent predictors for bacterial infection are reported in table .
ICU and hospital mortality rates were 20.2% (24 deaths) and 32.8% (39 deaths), respectively. PCT concentrations on ICU days 1 and 3 were not significantly different in survivors and decedents (Figure , panel B). Independent predictors of hospital mortality (Table ) were age (OR 1.03/y, 95%CI 1.001-1.06; P = 0.04) and invasive mechanical ventilation (OR 3.43, 95%CI 1.27-9.26; P = 0.01). Disseminated intravascular coagulation (DIC) at ICU admission was found to be protective against hospital mortality in the studied population (OR 0.96, 95%CI 0.94-0.99; P = 0.01).
Multivariate logistic regression with hospital survival as the outcome variable of interest