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C-Reactive Protein and Procalcitonin as Markers of Infection, Inflammatory Response, and Sepsis

Sierra, Rafael MD, PhD

Clinical Pulmonary Medicine: May 2007 - Volume 14 - Issue 3 - p 127-139
doi: 10.1097/CPM.0b013e3180555bbe
Respiratory Infections

Diagnosing sepsis and differentiating bacterial infections from other causes of inflammation constitute a challenge for clinical practice, especially in the intensive care unit. Many laboratory markers have been evaluated as diagnostic tests of bacterial infections and sepsis, but C-reactive protein (CRP) and procalcitonin (PCT) are at present the most studied and used indicators. The chief objective of this review is to appraise the role of CRP and PCT as diagnostic tests (biomarkers) of infections (especially pneumonia) and sepsis, by reviewing results from published studies. The diagnostic performance is not optimal because overall results of diagnostic studies on CRP and PCT as indicators of bacteria infections and sepsis have shown to be variable with wide ranges of sensitivity and specificity. Moreover, many of these diagnostic studies had methodological limitations that make it difficult to generalize their results. PCT tests appear to have somewhat higher overall diagnostic accuracy than that of the varied CRP tests, particularly in some clinical conditions. PCT also demonstrated to be a better severity indicator than CRP. Nevertheless, because of CRP kinetics, serial determinations of CRP can be useful for monitoring inflammatory activity and patient responses to antibiotic and sepsis therapies. Some novel markers could demonstrate to be more accurate for diagnosing severe infections and sepsis in the near future.

Blood levels of C-reactive protein (CRP) and procalcitonin (PCT) have been used and evaluated extensively as laboratory markers of infections (including pneumonia) and sepsis, especially in the critically ill patient. Like other diagnostic tests, these markers should fulfill certain methodological requirements that many studies do not report. A high number of diagnostic studies evaluating CRP and PCT as markers of infections and sepsis have been published, but their overall results were variable, with wide ranges of estimates of diagnostic accuracy, which makes it difficult to interpret and generalize. Nevertheless, both tests can assist in the diagnosis and monitoring of the therapy and response of bacterial infections and sepsis, particularly when they are used together with clinical signs, images, and other laboratory data.

From the Intensive Care Unit of University Hospital Puerta del Mar, University of Cádiz, Cádiz, Spain.

Address correspondence to: Rafael Sierra, MD, PhD, Intensive Care Unit of University Hospital Puerta del Mar, University of Cádiz, Cádiz, Spain. E-mail:

© 2007 Lippincott Williams & Wilkins, Inc.