Generality
Procalcitonin (PCT) is a biological marker of sepsis and septic shock, and of severe inflammatory reactions. At the plasma level, the finding of elevated PCT values is strongly suggestive of an inflammatory response to a "systemic bacterial infection.
What's this
Procalcitonin is the precursor of calcitonin. However, these two compounds have very distinct characteristics. Calcitonin is secreted exclusively by the C cells of the thyroid, following certain hormonal stimuli; PCT can be produced by different types of cellular components and by many organs in response to pro-inflammatory stimuli (eg bacterial endotoxins and cytokines).
The precise biological role of procalcitonin remains largely unknown, but it has recently been speculated that it may take part in the pathogenesis of sepsis.
Because it is measured
Plasma procalcitonin is measured as an early sepsis test. For this condition, PCT has a high degree of diagnostic accuracy and allows to anticipate therapeutic intervention. The examination is particularly useful when it is necessary to distinguish bacterial infections from those with other etiology or from non-specific inflammation.
PCT also allows the monitoring of septic patients being treated with antibiotics, establishing the resolution of the disease process or the risk of progression from severe sepsis (associated with organ dysfunction) to septic shock (sepsis with hypotension and alterations in perfusion). .
In addition to supporting the diagnosis of sepsis, procalcitonin has also been shown to be useful in monitoring the course and severity of the systemic inflammatory response.
Sometimes, PCT testing may be prescribed in patients with:
- Tissue damage due to trauma or surgery;
- Viral diseases such as pneumonia, in order to detect the development of secondary bacterial infections early.
The determination of procalcitonin may be requested together with other laboratory tests, such as blood culture, blood count with leukocyte formula, CSF analysis and measurement of C-reactive protein (PCR).
Normal values
Normally, procalcitonin plasma concentrations are less than 0.05 ng / mL.
In patients with sepsis or septic shock, however, these values can increase up to 1,000 ng / ml; procalcitonin reflects the severity of the disease and the course of inflammatory activity.
Usually, procalcitonin levels:
- Higher than 0.5 ng / ml are interpreted as abnormal values, suggestive of a septic syndrome.
- Between 0.5 and 2 ng / ml represent a range of uncertainty regarding the diagnosis of sepsis; in these cases, it is recommended to repeat the dosage after 6-24 hours, until the specific diagnosis is identified.
- Higher than 2 ng / ml are strongly suggestive of an inflammatory process with systemic involvement.
- Greater than 10 ng / ml are found almost exclusively in patients with severe sepsis or septic shock.
High Procalcitonin - Causes
- Plasma procalcitonin levels rise rapidly (within 6-12 hours) following an infectious insult with systemic consequences. PCT is significantly elevated especially in the first days of severe sepsis, septic shock and multiple organ dysfunction syndrome.
- In patients with non-bacterial systemic inflammatory response syndrome (SIRS), procalcitonin concentrations are usually less than 1 ng / mL. The values are maintained <0.5 ng / ml even in the presence of viral or localized infections, allergies and autoimmune diseases.
- Regardless of the presence of an infectious process, PCT levels can also be elevated soon after multiple trauma or surgery, in severe burns or in newborns (less than 48 hours old). In these cases, however, the return to the basic values is rapid; a possible second increase in procalcitonin could indicate the development of a septic episode.
- Procalcitonin may also be elevated in patients with severe or prolonged cardiogenic shock, severe organ perfusion disturbances, small cell lung cancer, or medullary thyroid (C-cell) carcinoma.
Low Procalcitonin - Causes
Low procalcitonin levels are not usually associated with medical problems and / or pathological consequences and are therefore not considered clinically relevant.
How it is measured
The procalcitonin test is performed on a blood sample taken from a vein in an arm.
Preparation
Before the procalcitonin test it is necessary to observe a fast of at least 8 hours, during which a moderate amount of water is allowed.
Interpretation of Results
- Daily variations in procalcitonin levels give indications on the course of the disease and the prognosis of the patient with sepsis. For this reason, the dosage of this parameter is indicated for the early and reliable diagnosis in all patients in whom the presence of a sepsis or a systemic inflammatory response is suspected.
- A high procalcitonin value should prompt antibiotic therapy to be initiated as soon as possible.
- Persistently elevated levels of PCT are associated with poor prognosis and are interpreted as failure of therapy or failure to eliminate the source of infection.
- If the plasma levels of procalcitonin are lower than 0.5 ng / ml, however, the presence of bacterial sepsis is unlikely.
