Use of Procalcitonin in LRTI and Sepsis Management

This is a verbatim transcript of an interview conducted with Dr Bui Thi Hanh Duyen, MD. PhD in July 2026. The transcript has been lightly edited for clarity.

Introduction

I am Dr Bui Thi Hanh Duyen, MD. PhD. I am the Head of the Intensive Care Unit at University Medical Centre Ho Chi Minh City, Vietnam.
I am also the Vice President of the Ho Chi Minh City Society of Asthma, Allergy and Clinical Immunology. Besides, I serve on several Executive Committees of national and local professional societies in critical care, respiratory medicine, and clinical nutrition.
I have more than 20 years of experience in critical care and am actively involved in clinical research, medical education, and international collaboration.

What is procalcitonin? What is the biological rationale for using procalcitonin (PCT) to differentiate and manage bacterial infections at the bedside?

Procalcitonin, or PCT, is a precursor of the hormone calcitonin. Under normal physiological conditions, PCT is produced mainly by the C cells of the thyroid gland. PCT concentration in healthy people is extremely low, typically less than 0.05 ng/mL.
However, during a systemic bacterial infection, bacterial endotoxins, especially lipopolysaccharide (LPS) from Gram-negative bacteria, together with pro-inflammatory cytokines such as TNF-α and IL-6, stimulate many extra-thyroidal tissues, including the liver, lungs, and intestine, to produce PCT.
In contrast, during viral infections, the host immune response is different. Viral infection stimulates the production of interferon-gamma, which suppresses PCT gene expression and inhibits PCT synthesis. Therefore, PCT usually remains low in viral infections, even when inflammation is significant.
In addition, PCT has favorable kinetics for bedside management. It begins to increase within 3 to 6 hours after bacterial infection and peaks at around 24 hours. If the infection is controlled with effective treatment, the PCT levels decrease.
Compared to other inflammatory biomarkers, procalcitonin has the highest AUC, sensitivity, and specificity compared with CRP and IL-6 in the study by Müller and colleagues.
However, procalcitonin can also rise in non-infectious conditions, like cardiogenic shock, acute pancreatitis, liver injury and post-operation. Note that procalcitonin can be low in certain infections, for example localized bacterial infections, during early stages, or in patients with a weakened immune system. So, we should combine PCT with clinical judgment to avoid missing a true infection or overdiagnosing one. It’s a real challenge in critical care.

How can clinicians safely use PCT kinetic trends to guide antibiotic de-escalation in severe LRTI and sepsis without risking patient relapse?

I think the safest way to use procalcitonin is to monitor the trend, not a single value, and always combine it with clinical assessment.
In my practice, I use PCT in three steps.
First, at the initial assessment, if a patient has severe low respiratory tract infection (LRTI) or suspected sepsis, I use PCT as additional information alongside clinical signs, imaging, cultures, organ dysfunction and SOFA score. I do not use PCT alone to decide whether to start antibiotics.
The updated Surviving Sepsis Campaign (SSC) guidelines recommend against using PCT to combine clinical assessment to start antibiotics in sepsis and septic shock. However, in my opinion, it still needs a PCT test to support diagnosis and to monitor treatment response thereafter.
Second, during treatment, I repeat PCT after 2 to 3 days to monitor the kinetic trend for evaluating the response to treatment. If PCT is reduced, patients may respond to treatment. In contrast, if PCT had an increased trend, the patient may not respond to treatment. So, I need to evaluate the clinical picture, the infectious source, recheck the culture, and assess the potential for antibiotic resistance.
Third, before stopping antibiotics, I always ensure that it is safe to do so. The patient’s clinical condition should be stable, source control should be adequate, and the PCT level should support de-escalation. There is no single PCT cutoff that applies to all infections. Generally, a PCT level < 0.5 ng/mL supports discontinuation of antibiotics in sepsis, whereas a cutoff < 0.25 ng/mL is commonly used for lower respiratory tract infections.
Therefore, PCT should never replace clinical judgment. SSC 2026 guidelines suggest using procalcitonin AND clinical evaluation to decide when to discontinue antibiotic over clinical evaluation alone in patients with sepsis and septic shock and adequate source control where optimal duration of therapy is unclear.
However, in complex infections, such as infective endocarditis, abscesses, or other deep-seated infections, I would not stop antibiotics based on a stable condition and a declining PCT level. Instead, I would continue treatment according to guideline-recommended durations.

Given the risk of overusing antibiotics in critical care settings, what antimicrobial stewardship interventions should be put in place urgently?

Every unnecessary day of antibiotic therapy increases the risk for the patients, including adverse drug reactions, such as acute kidney failure, liver injury, healthcare costs, fungal superinfection and selective pressure for antimicrobial resistance. So, we need antimicrobial stewardship in critical care settings. Antimicrobial stewardship requires a multidisciplinary team. It needs collaboration between ICU physicians, infectious disease specialists, microbiologists, clinical pharmacists, and the microbiology laboratory. However, in our ICU, antimicrobial stewardship includes ICU doctors, clinical pharmacists and specialists if needed. We use procalcitonin as an additional tool to support antimicrobial de-escalation. However, the final decision is always based on the patient’s overall clinical condition, microbiological findings, source control, and treatment response.
Several randomized studies have shown this benefit. For example, Gavazzi and colleagues conducted a trial in elderly patients with pneumonia. The study was published in 2022. The study showed that a PCT-guided strategy reduced the median duration of antibiotic therapy from 10 days to 8 days without affecting clinical recovery.

Overall, antimicrobial stewardship is not simply about reducing antibiotic use. It is about ensuring that every patient receives the right antibiotic, at the right time, at the right dose, for the right duration.

The views and opinions expressed by Dr Bui Thi Hanh Duyen, MD. PhD are her own views and opinions. Roche disclaims all liability in relation to these views and opinions.