Procalcitonin to Guide Antibiotic Utilization | Antibiotic Stewardship Program | UC Davis Health

Procalcitonin (PCT) is a biomarker of bacterial infection shown to reliably guide antibiotic use in some cases. It is acutely produced by a number of tissue types in response to bacterial toxins and various inflammatory mediators associated with bacterial but not viral infection. In some bacterial infections, particularly mild, localized disease, significant procalcitonin production may not occur. PCT therefore does not completely discriminate the presence or absence of a possible bacterial pathogen in all cases. PCT does, however, correlate with disease severity and may help discriminate those patients who would benefit from antibiotics from those who would not in some circumstances. Although it has been studied in a wide variety of populations, it has to date only been shown to consistently and safely guide clinicians in the initiation of antibiotics in non-septic patients with a clinically ambiguous lower respiratory tract infection (LRTI) and in the discontinuation of antibiotics in septic patients without a clear source of infection identified. Further guidance per below:

For non-septic patients with an ambiguous presentation for lower respiratory tract infection (LRTI), PCT may be used to aid in the decision whether or not to initiate antibiotics:

• If PCT < 0.10 ng/mlL – Antibiotics strongly discouraged
• If PCT 0.10–0.25 ng/mL – Antibiotics discouraged
• If PCT >0.25–0.50 ng/mL – Antibiotics encouraged
• If PCT > 0.50 ng/mL – Antibiotics strongly encouraged

If antibiotics are withheld consider a repeat PCT within 12–24 hours if the suspicion for a bacterial infection is high.

For patients with known or suspected sepsis antibiotics should not be delayed. PCT may, however, be used to guide the de-escalation of antibiotics if baseline PCT is elevated and a cause is not identified:

• If follow up PCT ≤ 0.50 ng/mL (non-LRT!) – Antibiotic discontinuation encouraged
• If follow up PCT ≤ 0.25 ng/mL (LRTI) – Antibiotic discontinuation encouraged
  OR
• If follow up PCT down ≥ 80% from peak – Antibiotic discontinuation encouraged

Consider ordering a PCT every 1–2 days in septic patients when a cause is not identified in order to guide antibiotic de-escalation per the above parameters.

Additional Notes:

PCT has not been validated in the significantly immunocompromised or pregnant populations. Most autoimmune disorders are not associated with elevated PCT levels.

False positive PCTs may result from major stressors (severe trauma, burns, surgery, shock), severe pancreatitis, aspiration pneumonitis, systemic fungal and parasitic infections, end stage renal disease (ESRD), medullary thyroid and other neuroendocrine tumors, extracorporeal circulation (ECMO), and receipt of certain immunomodulatory agents (granulocyte transfusions and antilymphocyte antibodies).

False negative PCTs may result from contained infections (abscess, empyema, etc.), intracellular bacteria (Legionella, Mycoplasma, etc), and if the PCT is drawn within the first 6–12 hours of infection.