What is being tested?

This test measures the amount of procalcitonin in the blood. Procalcitonin is normally made during the process of producing the thyroid hormone calcitonin. It is produced by special cells in the thyroid gland called C-cells and is present in low levels in the blood. However, it may also be made by other cells in the body when stimulated by certain disease processes, in particular bacterial infections. It is not particularly increased when a person has a viral infection.

Levels of procalcitonin in the blood increase rapidly and to high concentrations when a person has sepsis, particularly from a bacterial cause. Difference in stimulus gives procalcitonin the potential to be used to help detect severe bacterial infection at an early stage as well as to distinguish between a non-bacterial sepsis and another cause of a serious illness such as autoimmune disease that could be responsible for a systemic inflammatory response.

Other reasons for increased procalcitonin include tissue damage due to events such as trauma, surgery, pancreatitis, burns, heart attack; and rapid and severe organ (kidney, heart, lung etc) transplant rejection. It is also mildly elevated in renal failure.

How is it used?

The procalcitonin test is not available in all Australian laboratories, and research is still being carried out to help us understand its role and how it should be used in the management of patients. Studies have shown that it may help to discover whether a seriously ill person is developing sepsis. It has been studied mainly in emergency department or intensive care unit (ICU) patients who have symptoms that may be due to sepsis. In this circumstance, procalcitonin is best used during the first day the patient is seen by the doctor. It may be used later on to follow how the patient responses to treatment.

Procalcitonin may sometimes be requested with other tests such as a CRP (C-reactive protein), blood culture, FBC(Full Blood Count), or CSF (cerebrospinal fluid) analysis to help detect or rule out sepsis, bacterial meningitis, or bacterial pneumonia in those who are seriously ill and in children with a fever of unknown origin.

Occasionally, a procalcitonin test may be used to follow the effectiveness of antimicrobial treatment or for to make decisions on when to cease antibiotics.

When is it requested?

The procalcitonin test may be requested with other tests when a seriously ill person has symptoms that suggest that they may have sepsis or severe bacterial infection. Procalcitonin is normally used as an early detection test, requested within the first day of hospital admission. Symptoms of sepsis may include:

• Chills, fever
• Feeling sick (nausea)
• Rapid breathing, rapid heartbeat
• Confusion
• Decreased urine output

More severe complications of sepsis include inflammation throughout the body and formation of many tiny blood clots in the veins and capillaries. One or more organs may begin to stop working (multi-organ failure) and there may be a dangerous drop in blood pressure.

Procalcitonin may also be requested to follow antimicrobial therapy in persons suspected of having sepsis or to assist in determining whether an infection is likely to be of bacterial origin.

What does the result mean?

Low level of procalcitonin in a seriously ill person indicates a low risk of sepsis  but does not  completely exclude this possibility.  It may also indicate that the person's symptoms are likely due to another cause, such as transplant rejection, a viral infection, or trauma – post-surgery or otherwise.

High levels indicate a high possibility of sepsis or a higher likelihood of a bacterial cause for the symptoms. They also suggest a higher risk of progression to severe sepsis and then to septic shock.

Moderate elevations may be due to a non-infectious condition or due to an early bacterial infection and, along with other findings, should be reviewed carefully.

Decreasing procalcitonin levels in a person being treated for a severe bacterial infection indicates a response to therapy.

Is there anything else I should know?

The procalcitonin test is not a replacement for other laboratory tests. Rather it is additional information that may help earlier treatment.

Early detection of systemic bacterial infections, including bacterial pneumonia and bacterial meningitis, is important because they can be life-threatening and can be readily treated. However, the inappropriate use of antibiotics in cases where the illness is not bacterial in origin may cause delays in proper treatment and can encourage the development of antibiotic resistant organisms.

The procalcitonin test is being studied in additional populations, expanding beyond critically ill ICU patients. As more data are gathered, the clinical usefulness of procalcitonin will be better understood and its intended use(s) more fully defined. It is currently being explored for use in suspected COVID-19 patients to assist with detection of superimposed bacterial infection.

Common questions

• Should a procalcitonin test be performed every time a person is seriously ill?

No, it is generally only indicated when someone is seriously ill and the doctor suspects that the person may have sepsis or a severe bacterial infection. There is also still ongoing debate about the precise cut-offs that should be used to assist with diagnosis and treatment and thus procalcitonin is not uniformly requested in such situations.

More Information

RCPA Manual: Procalcitonin