Is Procalcitonin (PCT) recommended for viral fever?

Procalcitonin Testing in Viral Fever

Procalcitonin (PCT) testing is not recommended for viral fever, as PCT typically remains low in viral infections and is primarily useful for distinguishing bacterial from viral causes of fever. 1, 2

PCT in Viral vs. Bacterial Infections

• PCT is a biomarker that helps discriminate between bacterial and viral causes of fever:

  • PCT levels typically remain low (<0.1 ng/mL) in viral infections
  • PCT rises significantly (>0.5 ng/mL) in bacterial infections 2

• PCT interpretation guidelines:

  PCT Level	Clinical Interpretation
  <0.1 ng/mL	High probability of viral infection or non-infectious condition
  0.1-0.25 ng/mL	Low probability of bacterial infection
  0.25-0.5 ng/mL	Possible bacterial infection
  >0.5 ng/mL	High probability of bacterial infection
  >2.0 ng/mL	High probability of sepsis or severe bacterial infection

When to Consider PCT Testing

PCT testing may be appropriate in specific clinical scenarios:

• When bacterial co-infection is suspected in a patient with viral fever
• In critically ill patients with fever and no clear focus of infection, when the probability of bacterial infection is deemed low to intermediate 1
• To guide decisions about antibiotic therapy discontinuation rather than initiation 2

Limitations of PCT in Viral Infections

• PCT can be elevated during severe viral illnesses, including influenza and COVID-19, reducing its discriminatory power 2
• In a study of travelers with fever, only 1 out of 16 patients with proven viral infection had a marginally elevated PCT concentration 3
• PCT should always be interpreted in conjunction with clinical assessment, not as a standalone test 2

Comparison with Other Biomarkers

• PCT rises earlier (4 hours) than C-Reactive Protein (CRP) (12-24 hours) after infection onset 2
• PCT is more specific for bacterial infections than CRP:
  • PCT: sensitivity 80%, specificity 77% for bacterial infections
  • CRP: sensitivity 80%, specificity 61% for bacterial infections 2

Clinical Application

• For patients with suspected viral fever:

  • PCT testing is generally unnecessary unless bacterial co-infection is suspected
  • If PCT is measured and found to be <0.1 ng/mL, this supports a viral etiology 2, 4
  • If PCT is >0.5 ng/mL in a patient with presumed viral infection, consider bacterial co-infection 2

• For critically ill patients with fever:

  • The Society of Critical Care Medicine suggests measuring PCT (or CRP) when the probability of bacterial infection is low to intermediate 1
  • They recommend against measuring PCT when the probability of bacterial infection is high 1

Key Pitfalls to Avoid

• Do not use PCT as the sole determinant for initiating antibiotics in critically ill patients
• Do not delay antimicrobial therapy in septic patients while waiting for PCT results
• Remember that PCT values can be affected by certain conditions (renal failure, major trauma, surgery) that may lead to false elevations
• Do not use PCT routinely for all febrile patients, as this is not cost-effective

In summary, while PCT can be a valuable tool in distinguishing bacterial from viral infections, it is not recommended specifically for viral fever diagnosis unless there is concern for bacterial co-infection or when the etiology of fever is unclear.