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Procalcitonin is a protein substance produced by the body in response to bacterial infections. When bacteria invade the body, various cells release procalcitonin into the bloodstream. Measuring the level of procalcitonin through a blood test helps doctors determine whether an infection is caused by bacteria or viruses, which is crucial for deciding on appropriate treatment.

The procalcitonin test is particularly valuable in emergency and hospital settings. It helps distinguish between bacterial infections that require antibiotics and viral infections that do not. This is important because unnecessary antibiotic use can lead to antibiotic resistance and unwanted side effects. The test is commonly used to evaluate patients with respiratory infections, sepsis, or other serious infections. In healthy individuals, procalcitonin levels are very low or undetectable. However, when a bacterial infection occurs, levels can rise significantly within a few hours.

Healthcare providers use procalcitonin testing for several purposes. It helps in the early detection of severe bacterial infections and sepsis, a life-threatening condition where the body's response to infection causes widespread inflammation. The test also assists in monitoring how well a patient responds to antibiotic treatment. If procalcitonin levels decrease during treatment, it suggests the antibiotics are working effectively. Conversely, persistently high or rising levels may indicate that the infection is not responding to treatment or that complications have developed.

The procalcitonin test requires a simple blood sample drawn from a vein, usually in the arm. Results are typically reported in nanograms per milliliter. Low levels generally indicate no bacterial infection or a localized infection, while moderately elevated levels suggest a possible bacterial infection. Very high levels often indicate severe bacterial infection or sepsis. However, doctors interpret procalcitonin results alongside other clinical findings, symptoms, and test results to make accurate diagnoses and treatment decisions. Some non-infectious conditions can also cause elevated procalcitonin levels, so the test should not be used in isolation.