Procalcitonin (PCT)

Overview

Procalcitonin (PCT) is a peptide precursor of the hormone calcitonin, primarily produced by the thyroid C-cells under normal conditions. It plays a significant role in the body"s response to systemic bacterial infections and inflammation. PCT levels in the blood are typically very low in healthy individuals but rise rapidly in response to bacterial sepsis and severe infections, making it a valuable biomarker for detecting and monitoring these conditions. Tracking PCT helps guide antibiotic therapy decisions and assess infection severity, especially in critical care settings.¹²

Scientific Background

Biologically, procalcitonin is a 116 amino acid peptide precursor to calcitonin, a hormone involved in calcium homeostasis. Under normal metabolic conditions, PCT is produced mainly by thyroid C-cells and neuroendocrine cells at very low levels. However, during systemic bacterial infections or pro-inflammatory stimulation, many body tissues begin producing PCT in large quantities. This production is rapid, detectable within 2-4 hours, and peaks between 6-24 hours after infection onset. PCT modulates immune responses by influencing pro-inflammatory cytokines and acts as a chemokine to recruit immune cells to infection sites. It also affects vascular tone by regulating inducible nitric oxide synthase. PCT levels correlate with infection severity and can serve as a prognostic indicator for mortality risk in sepsis.¹²⁵

Measurement and Testing

PCT is measured in blood serum using immunoassays that detect its concentration, typically reported in nanograms per milliliter (ng/mL). Testing is most commonly performed in critical care or infectious disease settings to evaluate suspected bacterial infections or sepsis. Factors influencing results include the timing of sample collection relative to infection onset, presence of systemic inflammation, and non-bacterial causes such as trauma or surgery that may mildly elevate PCT. Testing is recommended when bacterial infection is suspected to guide antibiotic therapy and monitor treatment response.¹³

Reference Ranges

Normal PCT levels in healthy individuals are generally <0.05 ng/mL. Levels between 0.05 and 0.5 ng/mL may indicate localized infection or mild inflammation. Values above 0.5 ng/mL suggest systemic bacterial infection, with higher levels correlating with more severe sepsis or septic shock. Pediatric reference ranges are similar, though cutoffs for diagnosing sepsis in neonates and children often range from 2 to 2.5 ng/mL. Interpretation must consider clinical context, as non-infectious conditions can cause mild to moderate elevations. Age, immune status, and comorbidities may also influence baseline levels.²⁴

High Values

Elevated PCT levels are primarily caused by systemic bacterial infections such as sepsis, severe sepsis, and septic shock. Other causes include major trauma, surgery, burns, pancreatitis, cardiogenic shock, acute organ transplant rejection, and severe urinary tract infections in children. High PCT is associated with increased risk of mortality and indicates a strong inflammatory response. Symptoms related to high PCT levels often reflect the underlying infection or inflammatory condition, including fever, rapid heart rate, low blood pressure, and organ dysfunction.¹³⁴

Low Values

Low or normal PCT levels (<0.05 ng/mL) generally indicate absence of systemic bacterial infection. Causes of low PCT include viral infections, localized infections without systemic involvement, and non-infectious inflammatory conditions. Persistently low PCT in a febrile patient may help rule out bacterial sepsis and reduce unnecessary antibiotic use. Symptoms associated with low PCT are typically mild or related to non-bacterial causes.²³

Improving Biomarker Levels

Improving PCT levels involves treating the underlying bacterial infection effectively, often with appropriate antibiotic therapy guided by PCT trends. Lifestyle modifications to support immune health, such as adequate nutrition, hydration, and avoiding exposure to infectious agents, may help reduce infection risk. In critical care, PCT-guided antibiotic stewardship protocols help optimize treatment duration, reducing antibiotic overuse and resistance. No direct supplements alter PCT levels, but managing infection and inflammation is key.⁴⁵

Importance of Tracking

Monitoring PCT levels provides critical information for early detection of bacterial infections and sepsis, enabling timely intervention. It aids clinicians in distinguishing bacterial from viral or non-infectious causes of inflammation, guiding antibiotic use and reducing unnecessary exposure. Tracking PCT also helps assess infection severity and prognosis, informing clinical decisions in intensive care and emergency settings. Overall, PCT measurement improves patient outcomes by supporting targeted and efficient infection management.¹⁴

Disclaimer

The information provided in this document is for educational purposes only and does not constitute medical advice. It is essential to consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.