Critically evaluate the role of Procalcitonin (PCT) as a biomarker in the diagnosis and management of sepsis.
• PCT is synthesized physiologically by thyroid C cells but in sepsis has extrathyroidal origin from the inflamed/infected tissue
• The biochemical and clinical profile well described
• It is easy to perform (Blood test), not too expensive and provides a quick answer in about 30 minutes. Blood cultures can take up to 24 hours.
• PCT is no gold standard for infection. There number of reports of PCT elevation in non-septic SIRS, immediately after surgery and trauma.
• Data from meta-analyisis are conflicting, some suggesting it is superior to CRP, whilst others have concluded it is a weak biomarker in critical illness.
• PCT is not elevated in viral infection, autoimmune disorders and immunocompromised patients – hence empiric therapy still the way in these patients.
• PCT does not tell you the site of infection/inflammation. History, clinical examination and other investigations like CT scan can.
• PCT is a biomarker and cannot replace good history taking, systematic clinical examination, appropriate investigations for the source of sepsis.
Few prospective randomised studies using,PCT as a guide to antibiotic therapy, have showed that prescription rate and the cost of antibiotics was reduced significantly with similar outcomes compared to the conventional approach
(Mention of the recent Lancet paper (Jan2010 – ProRata study and its conclusions is worthy of extra credit).
If one were to approach this in a structured fashion, the answer would resemble the following:
- Introduction / definition:
- Procalcitonin is the prohormone of calcitonin, normally synthesised by the C-cells of the thyroid gland, but produced ectopically by lung and intestine in the context of sepsis. As such, it is an attractive biomarker, and has been the subject of interesting research.
- Procalcitonin may be useful in identifying occult infection; levels peak within 6-8 hours after the first appearance of endotoxin, and this it may identify patients with severe infection before blood cultures have time to incubate, and before more serious manifestations of sepsis have time to evolve.
- Procalcitonin may be useful in discriminating between bacterial and non-infectious causes of inflammation, as its synthesis is triggered by bacterial endotoxin
- Evidence: what the recent trials say
- The college answer quotes the PRORATA study which suggested that the use of procalcitonin could result in reduced antibiotic exposure.
- There are others:
- Overall, according to a recent meta-analysis (2015)
- "The optimal and most widely used procalcitonin cut-off value was 0.5 ng/mL with a corresponding sensitivity of 76% and specificity of 69%"
- The authors concluded that procalcitonin had a "fair" diagnostic accuracy for bacteraemia.
- According to an old meta-analysis (2004), it was more sensitive and more specific than CRP.
- Quick to perform the assay
- More specific for bacterial sepsis than CRP
- Optimal use requires serial measurements, which is even more expensive.
- Confounded by non-infectious conditions, such as...
- Extreme inflammatory stimuli:
- Massive tissue necrosis
- Tumour lysis
- Cardiac or major abdominal surgery
- Multi-organ system failure
- Treatment with T-cell antibodies
- End-stage renal failure (procalcitonin is chronically elevated)
- Extreme inflammatory stimuli:
- No value in assessment of fungal or viral infections
- No value in assessment of localised infections without a systemic response
- There is disagreement as to what the negative cutoff value should be.
- For the discrimination of infectious from non-infectious cause of fever, the clinical judgement of an ED physician is at least equally accurate, if not better.
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Delevaux, I., et al. "Can procalcitonin measurement help in differentiating between bacterial infection and other kinds of inflammatory processes?."Annals of the rheumatic diseases 62.4 (2003): 337-340.
Maniaci, Vincenzo, et al. "Procalcitonin in young febrile infants for the detection of serious bacterial infections." Pediatrics 122.4 (2008): 701-710.
Becker, Kenneth L., Richard Snider, and Eric S. Nylen. "Procalcitonin assay in systemic inflammation, infection, and sepsis: clinical utility and limitations."Critical care medicine 36.3 (2008): 941-952.
Limper, Maarten, et al. "The diagnostic role of procalcitonin and other biomarkers in discriminating infectious from non-infectious fever." Journal of Infection 60.6 (2010): 409-416.
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Wacker, Christina, et al. "Procalcitonin as a diagnostic marker for sepsis: a systematic review and meta-analysis." The Lancet infectious diseases 13.5 (2013): 426-435.
Hausfater, Pierre, et al. "Serum procalcitonin measurement as diagnostic and prognostic marker in febrile adult patients presenting to the emergency department." Critical Care 11.3 (2007): R60.
Bouadma, Lila, et al. "Use of procalcitonin to reduce patients' exposure to antibiotics in intensive care units (PRORATA trial): a multicentre randomised controlled trial." The Lancet 375.9713 (2010): 463-474.