Lab Tests

PROCALCITONIN 38224914​​

What is Procalcitonin (PCT)?

• PCT is a precursor of calcitonin synthesized in thyroid C cells and other tissues during bacterial infections.

• Typically undetectable in healthy individuals (<0.05 ng/mL), its levels rise significantly during systemic bacterial infections, mediated by cytokines such as interleukin-6 and tumor necrosis factor-alpha.

  • 0.05-0.10 ng/mL: Bacteremia unlikely. Consider viral or inflammatory causes based on clinical context.

  • 0.10-0.50 ng/mL: Bacteremia still unlikely but possible in specific contexts. Suggests localized bacterial infection.

  • >0.50 ng/mL: Bacteremia highly likely. Can also indicate noninfectious conditions like severe trauma, major surgery, or prolonged cardiogenic shock.

• PCT levels may be uninterpretable in patients with renal compromise. ​

• PCT levels do not appear useful in distinguishing bacterial cellulitis from its mimics. 30051724 ​

• Procalcitonin is specifically produced in bacterial infections due to the stimulation of parenchymal cells by pro-inflammatory cytokines like IL-6 and TNF-α, triggered by bacterial components. It is not elevated in viral infections due to suppression by IFN-γ, and it is minimally produced in noninfectious inflammatory conditions because the cytokine profile and triggers are different. This specificity makes PCT a valuable biomarker for bacterial infections. (ChatGPT)

Applications in Dermatology

Stevens-Johnson Syndrome (SJS)/Toxic Epidermal Necrolysis (TEN)

• PCT helps differentiate immune-mediated inflammation from bacterial sepsis in these conditions.

• Thresholds: ≥0.65 ng/mL indicates systemic bacterial infection in SJS/TEN

Necrotizing Fasciitis and other severe infections

• PCT can track infection severity and treatment response.

• ≥1 ng/mL is highly predictive of bacteremia in dermatologic inpatients.

• Declining PCT levels are associated with resolution of bacterial infections.

Limitations

• Elevated PCT levels can also occur in noninfectious conditions, such as:

  • Severe trauma, burns, major surgeries, or prolonged cardiogenic shock.

  • Chronic kidney disease and systemic lupus erythematosus.

  • Viral infections typically do not elevate PCT due to attenuation by interferon-gamma.

Clinical Integration

• Normal PCT with elevated ESR and CRP suggests non-bacterial cause of inflammation.

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