Procalcitonin Test and What the Results Mean

A procalcitonin test measures the risk of developing a potentially deadly bacterial infection called sepsis. Sepsis occurs when the body overreacts to a bacterial infection by releasing chemicals that can cause damaging inflammation. If your blood contains an abnormally high level of procalcitonin, a substance your body produces in response to a bacterial infection, it can indicate that you have sepsis or are likely to develop sepsis.

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 Is a Procalcitonin Test 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.

Who Is at Risk of Sepsis?

More than 1.7 million adults in the U.S. develop sepsis every year, according to the Centers for Disease Control and Prevention (CDC). While anyone who gets an infection can develop sepsis, certain groups have a higher chance of getting it because they are more susceptible to infections. They include:

• People older than 65
• Children younger than 1
• People with chronic conditions such as diabetes, cancer, and lung or kidney disease
• People with weakened immune systems
• People who recently had a severe illness
• Pregnant people
• People who previously had sepsis

What Do the Test Results Mean?

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, which occurs when blood pressure drops dangerously low.

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 what type of infection a person has. Most sepsis cases are caused by bacterial infections, but viral or fungal infections can also cause sepsis. Infections that cause sepsis can occur anywhere in the body, including the lungs, skin, or urinary tract.

If the symptoms are severe but the procalcitonin level is low, the cause is more likely viral. Higher procalcitonin levels indicate that the infection is probably bacterial. Knowing what type of infection you have can help ensure that the appropriate treatment is given and that if you have a virus, you aren't needlessly prescribed antibiotics.

A moderate to mildly high level of procalcitonin may also be due to something aside from an infection, such as tissue injury or a chronic condition that causes an elevation in procalcitonin.

What Causes 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)
• Cardiogenic shock (related to a heart attack)
• Organ transplant rejection
  
• Solid tumor infections (including certain cancers)

People who have certain conditions, such as COPD or chronic kidney disease, may also have elevated baseline levels of procalcitonin.

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.