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"Procalcitonin: A Very Useful Test" by Steven P. LaRosa, M.D.



Procalcitonin (PCT) is the prohormone of Calcitonin. It is also released by monocytes and macrophages rapidly in response to bacterial infections. Unlike the typically used biomarkers of inflammation (CRP and ESR), it does not rise in malignancies (or non-infectious inflammatory conditions with the following exceptions: medullary thyroid cancer, small cell lung cancer, administration of OKT3 and ATG, in the first 24 hours after trauma or surgery, in the first 48 hours of life, Adult Onset Still's Disease (AOSD), Wegener's granulomatosis and Kawasaki's Disease. As a clinical lab test PCT has been found to be useful in the following settings:

1) Antimicrobial Stewardship - numerous studies have shown that ability to use PCT as part of clinical decision making in stopping antibiotic therapy. In these studies antibiotic use mas discouraged if the PCT was < 0.5ng/ml and strongly discouraged if the PCT was < 0.25ng/ml. An important caveat is that a single PCT measurement may miss the peak level so a follow-up test should be performed in the setting of a normal value (<0.25ng/ml).

2) Monitoring of Infectious Disease- Following 48 hours of treatment for infection the procalcitonin should decrease 50% from baseline. A failure to achieve this decrease should raise questions about the diagnosis, antibiotic choice or need for a procedure to achieve source control of infection.

3) Suspicion of Bacteremia-A PCT at a cut of level of <0.5mg/ml is very effective at "ruling out" (negative likelihood ratio) bacteremia and has been used to avoid obtaining unnecessary blood cultures. Levels > 1-2ng/ml should raise a clinical suspicion of bacteremia in the appropriate clinical context.

4) Suspicion for Sepsis- Levels of PCT > or = 2 ng/ml have been found to be predictive of sepsis

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