Procalcitonin

What is being tested?
The test measures the amount of procalcitonin in the blood.
Procalcitonin is the precursor of the thyroid hormone calcitonin.
It is produced by special cells in the thyroid called C cells and is normally present in the blood at low levels. Procalcitonin can also be produced by other cells in the body in response to severe stress, such as sepsis. Procalcitonin does not increase, however, in local bacterial infections. Other types of stress include infections from other causes, tissue damage due to events such as trauma, surgery, pancreatitis, burns, cardiogenic shock (related to a heart attack) and acute organ transplant rejection.
Procalcitonin levels rise rapidly and considerably in the blood when a person has sepsis. They are not nearly as high when a person has a viral infection or another condition that could present with the same symptoms as sepsis. This gives procalcitonin the potential to be used to detect early sepsis, making it possible to distinguish a bacterial infection from another condition with similar symptoms.

How is the sample collected for testing?
A blood sample is obtained by drawing blood from a vein in the forearm.

Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.

1. How is it used?
2. When is it requested?
3. What does the test result mean?
4. Is there anything else I should know?

1. How is it used?
The procalcitonin test is fairly new, but it is being requested more and more often. Recent studies have shown that it can be used with good reliability to assess the risk that a seriously ill person will develop sepsis. It has mainly been studied in people who present to A&E or are admitted to intensive care units (ICU) with symptoms that could be due to sepsis. In the United States, the procalcitonin test has been approved by the FDA (Food and Drug Administration) for use, together with other laboratory tests, in the clinical assessment of seriously ill people, or to assess progression to severe sepsis and septic shock.
For diagnostic purposes, the test should be performed on the first day symptoms appear. It may later be used to assess the response to treatment. Procalcitonin may be requested together with other tests, such as CRP (C-reactive protein), blood cultures, a full blood count with differential and cerebrospinal fluid analysis, to diagnose or rule out sepsis, bacterial meningitis or bacterial pneumonia in seriously ill people and in children with fever of unknown origin. In some cases the procalcitonin test may be requested at intervals to check the effectiveness of antibacterial treatment.

2. When is it requested?
The procalcitonin test may be requested, together with other tests, when a seriously ill person has symptoms suggesting a probable severe systemic bacterial infection. It is requested on the first day of hospital admission as an early test for diagnosing sepsis.

Complications of sepsis may include:

• chills and fever
• nausea
• rapid breathing and rapid pulse
• confusion
• reduced urination

More severe symptoms include inflammation throughout the body and the formation of many tiny clots in the small blood vessels (DIC). One or more organs may stop working (multiple organ dysfunction), with a dramatic fall in blood pressure. Occasionally, the test may be requested at intervals to monitor antibacterial therapy in people with sepsis.

3. What does the test result mean?
Low procalcitonin levels in a seriously ill person indicate a low risk of sepsis but do not rule it out, nor do they rule out progression to severe sepsis and/or septic shock. Low concentrations may indicate a localised infection that has not yet become systemic, or a systemic infection that has been developing for less than six hours. Low procalcitonin levels may also indicate that the person’s symptoms are probably due to another cause, such as transplant rejection, a viral infection, or post-surgical or other trauma.
High blood procalcitonin levels, on the other hand, indicate that the symptoms are very likely due to sepsis. High procalcitonin levels also suggest a higher risk of progression to severe sepsis and then to septic shock. Moderate increases in blood procalcitonin may be due to a non-infectious condition or may reflect an early bacterial infection; together with other tests, procalcitonin values should then be carefully re-checked later. A fall in procalcitonin levels in a person who has been treated for a severe bacterial infection indicates a good response to therapy.

4. Is there anything else I should know?
The procalcitonin test is not a substitute for other laboratory tests; rather, it provides additional information that allows appropriate treatment to be started earlier. Early diagnosis of sepsis, including bacterial pneumonia and bacterial meningitis, is important because these conditions can be life-threatening but can readily be treated.
Inappropriate use of antibiotics when a disease is not bacterial in origin can delay the correct treatment, can encourage the development of antibiotic-resistant organisms and is an unnecessary expense. The procalcitonin test may also be useful in people other than seriously ill patients in intensive care units. As more data are collected, the clinical usefulness of procalcitonin will be better understood.

Should procalcitonin be tested every time someone is seriously ill?
No, it is generally indicated only when the person is seriously ill and the doctor suspects a severe bacterial infection in that patient.