PCT - fast and highly specific increase in bacterial infection and sepsis
One major advantage of PCT compared to other parameters is its early and highly specific increase in response to bacterial infections and sepsis. Thus, in septic conditions in creased PCT levels can be observed 3-6 hours after infectious challenge.
Low PCT values (<0.25 µg/L) in patients with clinical signs of infection (CAP, UTI) indicate a low probability for blood culture proof of bacterial infection, whereas elevated PCT values (>0.25 µg/L) seem to correlate with the bacterial load and positive blood culture result.
PCT levels in sepsis are generally greater than 1-2 µg/L and often reach values between 10 and 100 µg/L, or considerably higher in individual cases, thus enabling the diagnostic differentiation between various clinical conditions and a severe bacterial infection (sepsis) (Fig. 1).
Figure 1: PCT increase reflects the continuous development from a healthy condition to the most severe states of disease (severe sepsis and septic shock)
In healthy people, plasma PCT concentrations are found to be below 0.05 µg/L, but PCT concentrations can increase up to 1000 µg/L in patients with sepsis, severe sepsis or septic shock. PCT levels are usually low in viral infections, chronic inflammatory disorders or autoimmune processes.
Procalcitonin - best parameter for early sepsis diagnosis
Among the available laboratory parameters PCT has been shown to be the most useful. PCT has been demonstrated to be the best marker for differentiating patients with sepsis from those with systemic inflammatory reaction not related to infectious cause (Fig. 2).
Figure 2: Comparison of diagnostic performances of various markers for diagnosis of bacterial infection/ sepsis
PCT versus CRP
Summary receiver operating characteristic (SROC) curves comparing serum procalcitonin (PCT) and C-reactive protein (CRP) markers for detection of bacterial infections versus non-infective causes of inflammation. Each point contributing to the SROC curve represents 1 study (total number of studies: 12; total number of patients 905).
Only Procalcitonin improves accuracy of clinical sepsis diagnosis
Moreover, Procalcitonin (PCT) was shown to be the only laboratory parameter that made a significant contribution to the clinical diagnosis of sepsis (Figure 3). Information obtained from IL-6, IL-8 and CRP had no impact on the clinical diagnosis of sepsis on admission.
Figure 3: Accuracy of sepsis diagnosis based on a clinical model with and without PCT
Procalcitonin kinetics can be used to assess the effectiveness of treatment
As the septic infection resolves, Procalcitonin (PCT) reliably returns to values below 0.5 µg/L, with a half-life of 24 hours. Consequently, in vitro determinations of PCT can be used to monitor the course and prognosis of life-threatening systemic bacterial infections and to tailor the therapeutic interventions more efficiently (Figure 4). E.g., this has been demonstrated for the monitoring of patients with ventilator-associated pneumonia (VAP).
Figure 4: Typical course of PCT serum level according to patient's response to antibiotic treatment (n=109)
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PCT & Sepsis - Sepsis Epidemology - Sepsis Definition - PCT-Molecule & Kinetics - Reference Values