Procalcitonin rises in bacterial infection and falls quickly with treatment
Expansion
Procalcitonin
- The precursor of calcitonin, released from many tissues in bacterial infection under the influence of endotoxin and inflammatory cytokines, and suppressed by interferon gamma, which is why it stays low in most viral infections
- Rises within 3 to 6 hours, peaks at 12 to 24, and has a half life of about 24 hours, so it falls quickly with successful treatment
- Faster to rise and to fall than C reactive protein, which is the main practical advantage
Its established use is de-escalation: procalcitonin guided protocols safely shorten antibiotic courses in respiratory infection and in critical care without increasing mortality. The evidence for using it to withhold antibiotics in an unwell patient is much weaker, and it should never override clinical judgement.
Raised without bacterial infection: major surgery, trauma, burns, cardiac arrest, severe pancreatitis, cardiogenic shock, medullary thyroid carcinoma, small cell lung cancer, and the first days of life in neonates.
Falsely low despite bacterial infection: localised infection such as empyema, abscess, osteomyelitis and endocarditis, and very early presentation.
Other markers
- C reactive protein: cheap and universal, slower, and non-specific
- Lactate: a marker of tissue hypoperfusion, not of infection, and used for resuscitation and prognosis
- White cell count: crude, and can be low in severe sepsis
- Emerging markers such as presepsin and interleukin 6 are not in routine use
The diagnosis of sepsis remains clinical, defined as life threatening organ dysfunction from a dysregulated response to infection, and identified at the bedside by physiology and the NEWS2 score rather than by any laboratory value.