How the Procalcitonin Test Diagnoses Sepsis

Identifying Sepsis Before It Turns Deadly

A procalcitonin test is a type of blood test used to detect sepsis. Sepsis is a potentially deadly condition in which the body overreacts to a bacterial infection by releasing chemicals that can cause damaging inflammation. If left untreated, sepsis can become severe enough to cause organ failure and death.

The procalcitonin test can help quickly confirm if a person is experiencing sepsis, whether they are at risk of shock, and what types of drugs are going to be most effective. It can also help determine if some other condition is involved.

This article explains how the procalcitonin test works, how the results are interpreted, and what the test can and cannot tell you.

what is a procalcitonin blood test

Verywell / Laura Porter

How the Test Works

The procalcitonin test only requires a simple blood draw. It measures the amount of a substance called procalcitonin produced by many types of cells in the body. Procalcitonin levels can increase significantly when there is a bacterial infection or some form of tissue injury.

When a bacterial infection becomes systemic, meaning that it spreads throughout the body, procalcitonin levels can shoot up dramatically. The higher the level, the greater the likelihood of sepsis.

Other conditions can also increase procalcitonin but usually only to mild to moderate levels. Having elevated procalcitonin does not necessarily mean you have sepsis. It is simply an indication of a systemic infection that needs further investigation.

Other tests will be used to confirm the diagnosis. These may include blood cultures, a complete blood count (CBC), urinalysis, liver or kidney function tests, and imaging tests like ultrasound, computed tomography (CT), or magnetic resonance imaging (MRI).

Recap

A procalcitonin test measures the amount of substance called procalcitonin produced by the body in response to a bacterial infection or tissue injury. High levels of procalcitonin may be a sign of sepsis, but other tests are needed to confirm the diagnosis.

When the Test Is Used

The procalcitonin test is ordered when there is a suspicion of sepsis. It is frequently used in emergency rooms or intensive care units when people show signs of sepsis, including high fever, difficulty breathing, low blood pressure, and confusion.

The test is important because sepsis can be difficult to diagnose and doesn't always cause symptoms in the early stages. It is possible, for example, for procalcitonin levels to be low in the very early stages and increase steeply over the course of hours or days.

On the other hand, it is possible to have high procalcitonin levels and no clear symptoms in the early stages. It is only when the extreme inflammation begins to affect organs that severe symptoms will appear.

By testing procalcitonin levels early, doctors can prescribe treatment before the condition becomes serious or life-threatening.

Interpreting the Results

The procalcitonin test cannot diagnose infections. It can show your doctor if sepsis may be occurring, how severe it may be, and whether it is likely to progress to septic shock.

Although the results of a procalcitonin test should be interpreted by a doctor, they are generally described as follows:

  • Normal: 0 to 0.05 micrograms per liter (µg/L)
  • Low risk of sepsis: less than 0.5 µg/L
  • Possible sepsis: between 0.5 µg/L and 2 µg/L
  • Moderate to high risk of sepsis: between 2 µg/L and 10 µg/L
  • Severe sepsis: 10 µg/L or greater

The test can also help determine if an infection is more likely to be bacterial or viral. If the symptoms are severe but the procalcitonin level is low, the cause is more likely viral. This can ensure the right treatment is given and avoid the needless use of antibiotics.

Studies have shown that high procalcitonin levels in people with sepsis are associated with a greater risk of septic shock and death.

Causes of High Procalcitonin

While elevated procalcitonin levels can be a strong indication of sepsis, even minor infections like a tooth abscess can cause procalcitonin levels to rise. Even so, high levels usually point to sepsis.

When procalcitonin levels are in the low to moderate range, sepsis may be a possible cause. But other causes may be to blame. These include conditions that cause severe tissue injury, such as:

Any condition that decreases blood oxygen levels can also cause procalcitonin levels to rise even if there is no infection. These include conditions like asthma, pneumonia, COPD, and cardiac arrest.

Recap

Other conditions can cause procalcitonin levels to rise, including surgery, burns, non-septic inflammation, and non-systemic infections. Even so, the increases tend to be mild to moderate compared to sepsis.

Summary

A procalcitonin test is a type of blood test that can help diagnose sepsis and determine a person's risk of severe illness, shock, and death. Because sepsis worsens rapidly, an early diagnosis can ensure that the right medications are prescribed before the condition turns severe.

Based on how high or low the procalcitonin levels are, doctors can also get a better idea as to whether the cause is an infection or another condition. The test can also help differentiate between a bacterial and viral infection or a systemic or local infection.

A Word From Verywell

A procalcitonin level on its own only predicts a likelihood that an infection is present. The procalcitonin result is a guide, not a diagnosis.

People do not receive treatment based on a procalcitonin level alone. A battery of tests are needed, and the treatment is based on an interpretation of the results and the clinical judgment of the physician.

The true value of the procalcitonin level is that it can lead to the early treatment of sepsis. Treating the infection even a few hours earlier can make the difference between an illness that responds to antibiotics and one that lands you in intensive care.

Was this page helpful?
5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Cleland DA, Eranki AP. Procalcitonin. In: StatPearls [Internet]. Updated August 11, 2021.

  2. Samsudin I, Vasikaran SD. Clinical utility and measurement of procalcitonin. Clin Biochem Rev. 2017;38(2):59-68.

  3. National Institute of General Medical Sciences. Sepsis. Updated September 27, 2019.

  4. Chakraborty S. Do we need procalcitonin for sepsis? American Association for Clinical Chemistry. Published February 1, 2015.

  5.  Jin M, Khan A. Procalcitonin: uses in the clinical laboratory for the diagnosis of sepsis. Lab Med. 2010;41:173-7. doi:10.1309/LMQ2GRR4QLFKHCH9