Interpreting Procalcitonin Results
In a healthy individual, procalcitonin is unlikely to be elevated. It is important to note that procalcitonin does not diagnose a type of infection; rather, it indicates the likelihood that an infection may be present. The procalcitonin test itself does not diagnose an infection. Instead, the physician looks at additional tests and the patient's physical examination to determine if an infection is present, and how to treat the patient.
If sepsis is suspected, additional tests, such as blood cultures and a complete blood count (CBC), are often performed to determine if sepsis is present, and to determine what organism is causing the infection. In some cases, the procalcitonin is used to differentiate between a severe local infection, such as a respiratory infection, and an infection that has become systemic.
Local Infection VS Systemic Infection
A local infection is located in a specific part of the body; examples include a respiratory infection, a tooth infection or a bone infection. While the infection may be severe, it is isolated to one area of the body. A systemic infection is an infection that has entered the bloodstream and is moving to all areas of the body.
- A procalcitonin of 0-.05 µg/L is expected in a healthy individual.
- Procalcitonin levels of less than .5 µg/L may indicate an infection, but such a level is unlikely to be a systemic infection like sepsis. A local infection, such as an infected tooth or respiratory infection, could be present.
- A procalcitonin level between .5 - 2 µg/L indicates that a systemic infection is possible, but is not diagnostic of sepsis.
- Procalcitonin levels of 2-10 µg/L indicate sepsis is likely.
- Procalcitonin results of 10 µg/L or greater indicates a high likelihood of severe sepsis or septic shock.
Other Causes of Elevated Procalcitonin
There are additional reasons that an individual who does not have sepsis could have an elevated procalcitonin level. In newborns, the level is high without an infection. Injuries--particularly serious trauma or surgery--can also cause a high result without the presence of sepsis. Some medications, shock not caused by sepsis, cancer, and medical issues that may decrease the amount of oxygen that is able to reach organs can also cause elevation in procalcitonin levels.
Low Procalcitonin Levels With or Without SepsisIn addition to having high levels of procalcitonin without sepsis, it is possible for a patient who has sepsis to present with a low procalcitonin level. If the test is done very early in the course of the illness, the levels may be low, but will likely increase over the next few hours or days.
Low levels may also be detected when no source of infection is clearly in evidence; this may be due to an infection that is difficult to locate, such as infectious endocarditis, which is an infection in the tissue that surrounds the heart. A patient may have no symptoms of infection when the test indicates an infection is present.
What Does It All Mean?
In essence, a procalcitonin level on its own only predicts a likelihood that a type of infection is present. The procalcitonin result is a guide, not a diagnosis. Patients do not receive treatment based on a procalcitonin level alone: the entire scope of their current health is evaluated, and treatment is based on the clinical judgement of the physician. The patient is always evaluated for additional signs and symptoms of infection. For a patient who is examined early in the course of sepsis, and has a low procalcitonin level, repeating the test at a later time may reflect that sepsis is present.
The true value of the procalcitonin level is that it can lead to earlier treatment of sepsis, which can quickly become life-threatening. For an individual who is developing sepsis, being treated a few hours faster because of an elevated procalcitonin level can make the difference between an illness that responds quickly to antibiotics and an illness that is severe enough to require ICU level care.
PCT Reference Values. ThermoScientific. Accessed March, 2013. http://www.procalcitonin.com/default.aspx?tree=_2_4%0D
Procalcitonin. Lab Tests Online. Accessed March, 2013. http://labtestsonline.org/understanding/analytes/procalcitonin/tab/test
Procalcitonin usefulness for the initiation of antibiotic treatment in intensive care unit patients. Pub Med. Accessed March 2013. http://www.ncbi.nlm.nih.gov/pubmed/22809906