What is Procalcitonin?
Each hormone in the body has a precursor from which it is formed. In the case of calcitonin, a hormone produced by the thyroid gland, its peptide precursor is represented by procalcitonin. The main role of calcitonin as a hormone in the body is to maintain the homeostasis of the calcium metabolism.
Composed out of 116 amino acids, procalcitonin comes from the thyroid gland (it is produced in the parafollicular cells or the C cells). It is also produced at the level of the lung and the intestines, more specifically in the neuroendocrine cells.
In healthy people, it is practically impossible to determine the levels of procalcitonin in the blood stream, as these are usually under the common limit of detection (<0.01 μg/L).
However, the levels of procalcitonin increase when there is a stimulus causing inflammation in different parts of the body (most common – bacteria). In the situation that a proinflammatory stimulus is identified, the body will start to produce procalcitonin in increased levels (main production centers – lungs and intestines). Interestingly enough, the procalcitonin levels do not increase significantly when the stimulus is a virus or in case of inflammation does not have an infectious cause.
In patients who suffer from severe bacterial infections, with systemic symptoms being also present, the procalcitonin levels can increase as much as 100 μg/L. The half-life of procalcitonin in serum varies between 25 and 30 hours. Increased levels of procalcitonin have also been encountered in people who have overdosed on amphetamines (or analogs). These drugs are known to induce a systemic inflammatory response, leading to significantly high levels of procalcitonin (with no associated bacterial infection).
You must remember that, even though bacterial infections lead to high levels of procalcitonin in the body, this does not mean that the calcitonin levels are going to increase as well or that the serum levels of calcium are going to be reduced.
Increased levels of procalcitonin are not associated with any specific bacterial strains, this meaning that this measurement is useful for the identification of various bacterial infections. In the intensive care units, procalcitonin is often used for differential diagnosis; based on this measurement, doctors are able to eliminate the nosocomial infections that might appear in the newborns who have been hospitalized in an intensive care unit.
Uses of Procalcitonin
In patients who are suffering from severe bacterial sepsis, the measurement of procalcitonin can be used for the confirmation of the diagnosis. Procalcitonin is also useful in making the differential diagnosis, between the actual sepsis state and the one from the systemic inflammatory response syndrome. By measuring the procalcitonin levels, one can decide on the correct dosage of antibiotics, especially in those who suffer from infections localized at the level of the lower respiratory tract.
Keep in mind that procalcitonin is a biomarker with a higher specificity than other proinflammatory markers, such as cytokines. Thus, it can be highly useful in determining patients who suffer from sepsis, a generalized microbial infection affecting the entire body. Given the specificity for bacterial infections, procalcitonin is used for the rapid diagnosis of sepsis. The sooner the diagnosis is made, the sooner the treatment can be administered and the life-threatening symptoms can be eliminated. It is not certain why the procalcitonin levels increase in case of severe bacterial infections but, nevertheless, such measurements remain essential for the different diagnosis of various inflammatory processes.
Studies have shown that the measurement of procalcitonin might be useful in the administration of antibiotics in patients diagnosed with pneumonia. Depending on the level of procalcitonin identified in the blood, the doctor might decide whether or not to pursue the treatment with antibiotics in pneumonia patients. The values of procalcitonin can also help the doctor in deciding whether the infection is caused by bacteria or it has other, non-infectious causes. The fact that the measurement of procalcitonin is used to reduce the usage of antibiotics is a definite advantage; all over the world, there are a lot of people who follow treatments with antibiotics when it is not necessary. Overall, this translates into reduced costs for the treatment and the elimination of the risk related to increased drug resistance.
A study was performed on patients who were diagnosed with community-acquired pneumonia, caused by the infection with legionella pneumophila. This study concentrated on the measurement of procalcitonin levels. It was found that the increased levels of procalcitonin indicated a severe infection in the body, prolonging the period for which the person was admitted in the intensive care unit and increasing the risk for life-threatening symptoms or death. The same study has demonstrated a negative prognosis for the patients in which the levels of procalcitonin persisted at high values.
The conclusion of the study was that the measurement of procalcitonin offers valuable information about the state and prognosis of a patient; such measurement is considered superior in specificity, as compared to other measurements, such as CRP or the WBC. And, as it was already mentioned above, the measurement of procalcitonin allowed for the efficient administration of antibiotics, contributing to the reduction of hospital stays. For example, in patients who suffered from chronic obstructive pulmonary disease, the measurement of procalcitonin levels contributed to the reduction of days in the hospital from 7.1 to 4.8 days.
The measurement of procalcitonin is also extremely useful for the diagnosis of bacteremia, with this hormone having an increased sensitivity to bacteria present in the body.
Procalcitonin levels can be measurement in other medical conditions, including in malaria. Studies have shown elevated levels in malaria patients, especially if they suffered from complications. Procalcitonin levels can also be measured in patients who are suffering from pulmonary tuberculosis and in those who undergo chemotherapy for different types of cancer. It seems that the levels of procalcitonin levels can be useful in distinguishing bacterial infections caused by mycobacterium tuberculosis and pneumocystis jirovecii. High levels of procalcitonin have also been encountered in patients who have undergone organ transplants, suffering either from organ rejection or bacterial infections.