Test Information

Procalcitonin (PCT), a prohormone of calcitonin, is secreted by a variety of cell types in response to proinflammatory stimulation, specifically when bacterial in nature. Detection and monitoring of elevated PCT levels is thus useful in the setting of significant bacterial infections such as bacterial sepsis and pneumonia. This quantitative test is cleared by the FDA as an aid in the risk assessment of critically ill patients on their first day of ICU admission for progression to bacterial severe sepsis and septic shock. Published studies have also found the PCT assay to be useful in the diagnosis of other severe bacterial infections.

The interpretation of a PCT level depends on the nature of the suspected bacterial infection, and must be made in the context of clinical signs and symptoms and the results of other diagnostic studies. Generally speaking, a PCT level of < 0.10ng/mL confidently rules out a significant local or systemic bacterial infection in patients >72 hours in age, while a value >2.00ng/mL is highly supportive of bacterial sepsis and/or septic shock. Depending on the circumstances, a PCT value >0.50ng/mL is supportive of a significant bacterial infection when consistent with clinical signs and other diagnostic studies. (See below for specific interpretations.*)

The interpretation of neonatal PCT levels is more complex, since PCT levels in healthy neonates is low at birth, rises as much as 20-fold by 24 hours of age, and then drops into the adult reference range by 72 hours of age.

(See graph: Procalcitonin (PCT) Levels in the Neonate)

Nevertheless, neonatal PCT levels predictably rise above the baseline in response to severe bacterial infections much as they do in older patients.  

Successful antibiotic therapy leads to a drop in PCT level, with a half-life of approximately 24 hours. Serial PCT measurements are therefore useful in monitoring the effectiveness of treatment. No accepted risk score has been developed for PCT, but a level of >10ng/mL indicates a high likelihood of bacterial severe sepsis or septic shock.   

Non-infectious severe inflammatory reactions may lead to an increase in PCT, but the return to normal levels in these instances is usually rapid. In general an elevated PCT is more specific for severe bacterial infection than acute phase reactants such as C-reactive protein (CRP). There is no international PCT standard; PCT levels generated in different labs should therefore not be compared as the methodology and reference intervals may differ.