The absolute level of PCT concentrations increase with increasing severity of disease. However, as an expression of individually different immune responses and different clinical situations, the same focus of infection may be associated with varying individual elevations in PCT concentrations.
The optimal cut-off values ranges of Procalcitonin (PCT) are variable and dependent on
- The clinical setting (eg, emergency room, ICU, post-operative or trauma patients)
- The site and extent of the infection (eg, RTI, meningitis, abdominal infection)
- Co-morbidities (eg, immunosuppression)
- The clinical implications drawn (eg diagnosis, prognosis, antibiotic stewardship).
Therefore, clinicians should use the PCT results in conjunction with other laboratory findings and clinical signs of the patient and interpret the concrete values in the context with the clinical situation of the patient (see also Note below). The reference ranges below are therefore given for orientational purpose only.
Increased PCT levels may not always be related to systemic bacterial infection.
There are a few situations described where PCT can be elevated by non-bacterial causes. These include, but are not limited to
- Neonates < 48 hours of life (physiological elevation) 3 (see reference values in Table 1 and Figure 9)
- The first days after a major trauma, major surgical intervention, severe burns, treatment with OKT3 antibodies and other drugs stimulating the release of pro-inflammatory cytokines
- Patients with invasive fungal infections, acute attacks of plasmodium falciparum malari
- Patients with prolonged or severe cardiogenic shock, prolonged severe organ perfusion anomalies, small cell lung cancer, medullary C-cell carcinoma of the thyroid.
Low PCT levels not always indicate absence of bacterial infection.
Falsely low PCT levels in the presence of bacterial infection may accour eg. in case of
- Early course of infections
- Localised infections (see chapter PCT & Infection)
- Subacute infectious endocarditis.
Serum or plasma PCT concentrations of healthy persons measured with a high sensitive assay revealed to be below 0.05 ng/ml (97.5% percentile).
PCT reference range in neonates
Early and reliable differentiation of infected and non-infected newborns is possible with PCT determination directly after birth from cord blood when neonatal infection is suspected. A value <0.5 ìg/L practically excludes the presence of infection (calculated best cut-off 0.6 ìg/L with a negative predictive value of 99% and a post-test probability of 0.001%).
After birth the PCT values of the newborn increase over the first 24 hours and stay elevated during the first 2 days of life. Therefore separate, well-defined reference ranges apply to new born infants at different hours of age during the first 48 hours of life (see Figure below to the left). However, also during these first 2 days of life, the PCT values of newborns suffering from early sepsis are significantly higher than those of non-infected newborns (see Figure below to the right), so that PCT can be used for sepsis diagnosis. The adult reference range applies from day 3 after birth.
Chiesa C et al. Clin Infect Dis 1998, 26: 664-672
Chiesa C et al. Clin Chem 2003, 49(1): 60-68
Joram N et al. Eur J Clin Microbiol Inf Dis 2011, Feb 12