Introduction to Biomarkers and Procalcitonin

Infections can be caused by a diverse range of microorganisms that produce a wide variety of clinical conditions. These can vary greatly in both patient-rated symptoms and severity, often causing difficulty in diagnosing the infection.

When a clinical diagnosis is not obvious, diagnostics and prognostic tools can be incorporated to help reach a diagnosis and make the most accurate decisions at each moment of a patient´s care. Measuring white blood cells (WBC, WCC), C reactive protein (CRP), and lactate are among the routinely used biomarkers in clinical practice for patients with suspicion of infection or suspicion of sepsis.

We know in clinical practice it can be challenging to differentiate between different types of infection e.g. viral pneumonia from bacterial pneumonia, particularly in extremes of age. The recent COVID-19 pandemic resulted in this confusion, meaning patients often got unnecessary antibiotics due to the uncertainties clinicians faced when they encountered individuals severely ill with SARS-CoV-2 infection. Recently, procalcitonin (PCT) gained interest as an antimicrobial stewardship tool.

Despite its limitations, which will be addressed throughout the course, PCT has been extensively studied and recognised as a valuable biomarker to support diagnosis and guide therapy in infectious diseases. PCT has been shown to correlate with SOFA score and outcomes in sepsis patients, which has helped it retain its clinical value over the past 20 years – particularly after the recent redefinition of sepsis as a clinical syndrome.

PCT measurement can prove useful in reducing inappropriate or unnecessary use of antimicrobial therapies when applied to the right patient population in the right clinical setting. Clinicians should develop algorithms to suit their local practice based on international guidelines and cut-off values. Implementing a regular audit programme would enable clinicians to monitor clinical practice consequences, antibiotic saving and impact on patient outcomes and cost.

Like any other diagnostics, misuse of PCT may lead to high volumes of useless determinations. This can lead to the perception of limited utility of PCT by clinicians and the risk of wasting its positive and negative predictive values. Therefore, it is important for clinicians to know the optimal areas of use for PCT, as highlighted in a recent international consensus paper, to preserve PCT as a tool in the antibiotic stewardship setting.

References are available in the see also section below, if you wish to read more about this topic.