Procalcitonin for Bacterial Infection

Procalcitonin (PCT) is the precursor peptide of calcitonin which under normal circumstances is secreted by thyroid C-cells in response to hypercalcemia. PCT is normally undetectable in serum, but is produced in large quantities by many organs & cells in response to severe inflammation, especially in the setting of bacterial infection.

The association between elevated PCT and bacterial infection was first described in 1993, and the assay has been used clinically in Europe for many years. PCT rises within 2-4 hours of onset of systemic bacterial infection and peaks within 6-24 hours. Sensitivity and specificity range from 60-90% for predicting sepsis. PCT testing is being used to differentiate bacterial versus viral infections and reduce antimicrobial therapy, especially in patients with lower respiratory tract infections and sepsis.

Unlike other markers of inflammation (e.g. CRP & ESR), PCT is thought to be more specific for bacterial infection. Its predictable half-life of 24 hours makes it useful for serial monitoring of therapeutic response. PCT level of a patient who is responding to antibiotic therapy should decrease by half every 24 hours. Also, unlike other inflammatory markers, PCT is usually low in viral infections, chronic inflammation & autoimmune disease. PCT level reportedly correlates with severity of inflammation. For example, in the appropriate clinical setting, PCT >2 ng/mL predicts sepsis or severe localized bacterial infection, and a level of >10 ng/mL is indicative of septic shock. Mortality is increased when PCT levels are >20 ng/mL.

A meta-analysis of 8 studies with 3431 patients indicated that PCT monitoring of patients with lower respiratory tract infections resulted in a 31% decrease in antibiotic prescriptions and a decrease in antibiotic therapy duration of 1.3 days (Li H et al. Antimicrob Agents Chemother 2011;53:379-87). Likewise, an international multicenter study including 1759 patients documented an 20% reduction in duration of antibiotic administration, when an algorithm for PCT-guided therapy was followed (Albrich, et al. Arch Intern Med 2012;172:715-723).

PCT has limitations and may be elevated in clinical situations other than systemic bacterial infections. Therefore it is imperative that PCT testing is used & interpreted in conjunction with other clinical & laboratory data. PCT can also be elevated by:

  • Major trauma, major surgery, and severe burns.
  • Cardiogenic shock and multiorgan failure with hypoperfusion.
  • Medullary thyroid cancer & small cell lung cancer.
  • Untreated end-stage renal failure. Stable hemodialysis or peritoneal dialysis patients have PCT levels comparable to healthy adults with normal renal function.

Specimen requirement is one red top tube of blood. Results are reported quantitatively with reference range <0.1 ng/mL.


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