COVID-19 has escalated into a worldwide pandemic and resulted in millions of severe cases and fatalities. Developing triage and treatment strategies depends heavily on recognizing high-risk patients at an early stage. Under normal physiological conditions procalcitonin (PCT) exists as a precursor protein without any recognized physiological function. This protein becomes crucial for both diagnostic and pathophysiological purposes when the body enters a pathological state. Research demonstrates severe COVID-19 patients experience a remarkable increase in procalcitonin production and release which could serve as a dependable predictive marker.
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Physiological Production and Conversion of Procalcitonin
When the body is infected with bacteria, PCT levels will increase significantly, so it is often used as a biomarker for bacterial infection to help distinguish viral from bacterial infections.
| Item |
Normal state |
Infection/inflammatory state |
| Source |
Thyroid C cells |
Multiple organ neuroendocrine cells |
| Function |
Converted into calcitonin to regulate calcium metabolism |
No direct physiological activity, only an inflammatory marker |
| Blood concentration |
Extremely low (<0.05ng/mL) |
Significantly elevated (can be >10ng/mL) |
| Clinical significance |
No diagnostic value |
Sensitive indicator for judging infection/inflammation |
Under Normal Circumstances
- Source: PCT is mainly synthesized by thyroid C cells in normal people.
- Conversion process: PCT → Calcitonin → Regulate calcium and phosphorus metabolism. In this process, PCT is completely converted into calcitonin, so the PCT concentration in the blood is extremely low (<0.05 ng/mL).
Function
Under normal physiological conditions, calcitonin participates in the regulation of calcium metabolism, but PCT itself does not play a physiological role.
Changes in PCT under Pathological Conditions
- The origin of PCT is no longer limited to thyroid C cells, but is widely expressed by neuroendocrine cells in multiple organs such as the lungs, liver, kidneys, and intestines.
- At this time, PCT is no longer a physiological regulator, but an acute phase response protein that reflects a systemic inflammatory response.
The Relationship between Procalcitonin and COVID-19
Although COVID-19 is caused by the SARS-CoV-2 virus, the role of PCT in disease monitoring has been increasingly valued, especially in the following aspects:
Determine whether there is bacterial co-infection
The PCT level of patients with mild or moderate COVID-19 is usually normal or slightly elevated. If PCT is significantly elevated, it may indicate secondary bacterial infection, such as pneumonia or sepsis.
Predicting the severity of the disease
Several studies have shown that the PCT level of patients with severe or critical COVID-19 is significantly higher than that of patients with mild symptoms. Elevated PCT is associated with complications such as cytokine storm and multiple organ failure.
Assisting clinical decision-making
PCT can be used to dynamically monitor disease progression or treatment response.
Procalcitonin Used as a Predictive Marker for COVID-19
Procalcitonin (PCT) is a commonly used blood biomarker for evaluating bacterial infection and disease progression. It is also used to guide the administration of antibiotic therapy in patients with severe respiratory tract infections and sepsis. PCT is also often elevated due to the inflammatory cascade caused by the cytokine storm in COVID-19 patients. Although procalcitonin is not a specific indicator of COVID-19 infection, it has important clinical significance in determining whether there is a concurrent bacterial infection, predicting the severity of the disease, and guiding the use of antibiotics. As a dynamic monitoring indicator, PCT can provide an important basis for formulating treatment strategies.
References
- Velissaris, D., et al. Procalcitonin and sepsis in the Emergency Department: an update. European Review for Medical & Pharmacological Sciences. 2021, 25(1).
- Kumar, A., et al. Procalcitonin as a predictive marker in COVID-19: A systematic review and meta-analysis. PloS one. 2022, 17(9): e0272840.
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