Protocol for Serum Procalcitonin testing in Medical Admissions (for adults only).  

• Flowchart
• Background
• Indications for testing
• Practicalities

Back to top

Background

Procalcitonin (PCT) is a protein produced in the C-cells of the thyroid gland in levels not normally detectable in the blood. However, during bacterial infection, toxins and cytokines stimulate production of PCT in other cells, leading to rapid increase in plasma levels in around 3-4 hours. It is therefore a sensitive and specific biomarker of bacterial infection.  It has a short half-life of around 24 hours and is not dependent on renal function.

PCT has been used to differentiate bacterial infection from viral infection, fungal infection, autoimmune disease and other causes of SIRS.  Sensitivity and specificity vary between infection site, patient group and cut-off level.  Use of PCT in acute medical patients where bacterial infection was suspected has been shown to safely reduce antibiotic use, without resulting in increases in mortality or clinical failure8. Use of PCT in acute respiratory infection has been shown to be associated with lower mortality, lower antibiotic consumption and lower rates of antimicrobial side effects9.

In patients outside of the critical care setting, there is insufficient evidence to recommend the use of serial procalcitonin measurements to guide antibiotic duration. For patients in critical care, please refer to the “Enhanced Antimicrobial Stewardship with the introduction of Procalcitonin to guide antibiotic duration in Adult Critical Care” guideline (http://nww.lhp.leedsth.nhs.uk/common/guidelines/detail.aspx?ID=5058).

Back to top

Indications for testing

PCT levels are used to guide antibiotic initiation in the following situations;

• Infection is suspected but not confirmed and the criteria for sepsis are not met
• Patients with suspected COVID-19, community acquired or healthcare associated pneumonia
• Initiation or discontinuation of antibiotics is being considered
• On advice from a Microbiologist or Infectious Diseases Specialist

Procalcitonin testing should not be used;

• Where bacterial infection is highly likely or proven and antibiotics are indicated regardless of PCT result
• Patients who meet sepsis criteria
• Patients with significant positive cultures
• Severely immunocompromised patients
• Patients with cystic fibrosis, bronchiectasis or active tuberculosis

Procalcitonin levels will be increased in the following conditions and therefore should not be used to guide antibiotic therapy;

• Surgery within previous 3 days
• Treatment that acts upon the pro-inflammatory CK cascade (OKT3, injection therapy TNFα, IL-2 and anti-lymphocyte globulins)
• Some cancers; medullary CT-cell cancers of the thyroid, pulmonary small-cell carcinoma and bronchial carcinoma
• Prolonged cardiogenic shock or haemorrhage
• Severe hepatic dysfunction
• Rhabdomyolysis

There is insufficient evidence for use of PCT monitoring in pregnant women so testing is not recommended.

Back to top

Practicalities

Blood should be sent in a yellow-top tube to biochemistry.  Turn-around time is expected to be within 6 hours.  The request for PCT may be able to be ‘added-on’ to samples taken within 6 hours dependent upon laboratory capacity. Tests cost ~£14 each.