Procalcitonin Blood Test Results and What They Mean

Procalcitonin is a substance your body produces in response to a bacterial infection. A procalcitonin test measures how much procalcitonin is in your blood.

High levels of procalcitonin can mean you have a serious bacterial infection called 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 and whether they are at risk of shock. The test can also help determine if some other condition is involved and whether or not you need to be treated with antibiotics.

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 Test?

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).

When the Procalcitonin 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.

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 low to moderate, sepsis may be a possible cause. But other causes may be to blame. These include conditions that cause severe tissue injury, such as:

• Severe trauma
• Burns
• Surgery
• Pancreatitis (inflammation of the pancreas)
• Meningitis (inflammation of the tissues that surround the brain)
• Endocarditis (inflammation of the heart)
• Cardiogenic shock (related to a heart attack)
• Organ transplant rejection
  
• Severe urinary tract infections in children
• Solid tumor infections (including certain cancers)

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.

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 is 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.