[tabby title="Overview"] Procalcitonin Test: Overview Procalcitonin (PCT) is the precursor of the hormone calcitonin and is mainly produced by the thyroid. Procalcitonin is a so-called acute phase reactant, rising in response to tissue inflammation and injury. Outside the thyroid, PCT is secreted by the lungs, intestines and other tissues in increasing amounts in response to bacterial endotoxin in the bloodstream. This makes PCT a more specific biomarker for infection than acute phase reactants like erythrocyte sedimentation rate or C-reactive protein, or negative acute phase reactants like prealbumin. Procalcitonin tests are immunoassays, often with short turnaround times (minutes to hours). PCT can be detected in blood within 2 to 4 hours of infection. Procalcitonin levels peak within 6 and 24 hours and may be detected for up to 7 days. PCT's half-life is approximately 24 hours. A PCT normal level is zero; any PCT elevation may be considered abnormal. A PCT test costs about $25. Millions of patients annually are evaluated in emergency departments or other health care settings with signs and symptoms consistent with infection, but these evaluations are often inconclusive. The PCT test might help guide initial testing and treatment for patients with suspected infections. A PCT assay has been approved by the U.S. FDA for: