Procalcitonin (PCT) is a protein and biomarker used in healthcare to identify and monitor systemic bacterial infections, including sepsis. PCT functions as a prohormone to calcitonin, but unlike calcitonin, which is synthesized in the C cells of the thyroid gland and regulates calcium homeostasis, PCT is produced in multiple tissues during systemic inflammation, particularly during bacterial infections.
In viral infections, PCT levels usually remain low, making procalcitonin useful for distinguishing between bacterial and viral infections. PCT is also used to guide antibiotic therapy as falling levels may indicate effective treatment and thus reduce unnecessary antibiotic use.
Physiological function
Under normal physiological conditions, PCT levels are very low (below 0.05 µg/L) because the prohormone is only produced in the thyroid gland and converted to calcitonin. In bacterial infection or sepsis, extra-thyroidal synthesis of PCT is instead induced in the liver, lungs, intestines and other organs. This occurs through stimulation by pro-inflammatory cytokines such as IL-1β, IL-6 and TNF-α, as well as by bacterial endotoxins (lipopolysaccharides, LPS).
In contrast, viral infections stimulate endogenous interferons, such as IFN-γ, which inhibit PCT production, causing the level in the blood to remain low.
Main functions of Procalcitonin
- Indicator of bacterial infections – PCT rises significantly in systemic bacterial infections and sepsis.
- Distinguishes bacterial from viral infections – Remains low in viral infections, making the test useful for diagnostics.
- Useful in sepsis diagnostics – Provides a rapid and sensitive indication of the severity of the infection.
- Guide for antibiotic therapy – Can be used to assess the need for antibiotics and monitor the effectiveness of treatment.
- Rapid kinetics – PCT increases within 2–6 hours in bacterial infection and has a half-life of approximately 24 hours, making it a dynamic marker for monitoring infections and treatment effectiveness.
Procalcitonin Analysis in Healthcare
S-Procalcitonin is used to diagnose, risk stratify, and monitor severe bacterial infections and sepsis. Since PCT is elevated in systemic bacterial infections but low in viral infections, the test can contribute to rational antibiotic use and reduce antibiotic resistance.
Commonly used uses for S-Procalcitonin
- Suspected sepsis – Helps assess the severity of the infection and differentiate sepsis from non-infectious inflammatory conditions.
- Pneumonia and respiratory tract infections – Used to distinguish bacterial from viral etiology and to guide antibiotic therapy.
- Postoperative monitoring – Identifies secondary infections after surgical procedures, especially in complicated abdominal or thoracic surgeries.
- Febrile conditions in immunosuppressed patients – Helps in the evaluation of neutropenic fever, for example in cancer patients undergoing chemotherapy.
- Urinary tract infections with suspected pyelonephritis – Provides support in the diagnosis of severe urinary tract infection, where clinical findings are uncertain.
- Antibiotic management – When monitoring the effect of treatment, falling PCT levels may indicate that antibiotics can be started out, which reduces the risk of resistance development.
Reference values and interpretation of S-Procalcitonin
Normal PCT values for healthy individuals are usually below 0.05 µg/L. Elevated concentrations may indicate a bacterial infection or sepsis depending on the degree of elevation.
| S-Procalcitonin (PCT) | Interpretation |
|---|---|
| Test result lower than 0.05 µg/L | Normal level, no bacterial infection suspected. |
| 0.05–0.5 µg/L | Slightly elevated level, can be seen in mild infections, postoperatively or in local inflammation. |
| 0.5–2.0 µg/L | Elevated level, indicates systemic bacterial infection, but sepsis is not certain. |
| Test result above 2.0 µg/L | Strongly elevated level, indicates likelihood of sepsis or more severe systemic infection. |
Interpretation of PCT values in clinical practice
- PCT below 0.05 µg/L – No significant bacterial infection. Antibiotics are usually not necessary.
- PCT 0.05–0.5 µg/L – Can be seen in mild infections, postoperatively or in autoimmune diseases. Clinical context is important.
- PCT 0.5–2.0 µg/L – Indicates bacterial infection, but other inflammatory processes can also cause some elevation.
- PCT above 2.0 µg/L – High probability of sepsis, especially with symptoms such as fever, hypotension or organ involvement. Requires urgent investigation and possible treatment.
- Decreasing PCT values during antibiotic treatment indicate effective therapy and can guide the decision to discontinue antibiotics.
- PCT may be falsely elevated in severe trauma, surgery, burns, malignancies or renal failure.