Procalcitonin as a marker of infection in critically ill patients

Objective

To determine the value of procalcitonin (PCT) as a marker of infection in critically ill patients with systemic inflammatory response syndrome (SIRS) at any time during their ICU stay.

Materials and methods

We prospectively studied 23 patients that suffered SIRS after their admission in a 23-bed general ICU. Patients were divided in two study groups according to the time of the onset of SIRS. Group A: eight patients (APACHE II score 19 ± 6, age 56 ± 18 years) who had SIRS within 7 days after admission; and group B:14 patients (APACHE II score 17 ± 8, age 51 ± 19 years) who had SIRS after the first week of stay in ICU. Clinical and laboratory measurements recorded for three consecutive days included temperature (T), white blood count (WBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) and PCT. Infection was confirmed by positive blood, bronchoalveolar lavage, urine or other body fluid cultures.

Statistical analysis

To evaluate differences between studied groups, a t test was used. Cutoff values for PCT were determined using Youden's index. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of PCT were also estimated.

Results

Infection was confirmed in four (50%) patients in group A and in 11 (79%) patients in group B. the serum concentration of CRP, WBC, ESR and T was similar in both groups, as well as between septic and nonseptic patients within each group. The PCT value in group A did not differ significantly in comparison with group B (7.1 ng/ml vs 0.5 ± 0.3 ng/ml, P = 0.06). However, septic patients in group A had significantly increased PCT values compared with septic patients in group B (9.48 ± 11 ng/ml vs 0.49 ± 0.3 ng/ml, P < 0.05). The best cutoff value, sensitivity, specificity, PPV and NPV for PCT in groups A and B are presented in Table 1.

Table 1

Conclusions

During the first week of recovery in the ICU, critically ill septic patients have increased serum PCT levels. However, PCT cannot reliably distinguish infection in patients with SIRS. On the contrary, in prolonged ICU stay, the diagnostic value of PCT in differentiating septic from nonseptic patients increases. It is important to notice that the PCT value in late septic patients is very close to considered normal values. Further studies are needed to determine the prognostic value of PCT in critically ill patients.