Shingles Does Not Typically Raise Procalcitonin
Herpes zoster (shingles) is a viral infection and does not typically cause clinically significant elevation in procalcitonin levels, as procalcitonin remains low in viral infections and is primarily elevated in bacterial infections.
Understanding Procalcitonin in Viral vs. Bacterial Infections
Procalcitonin (PCT) is specifically designed to differentiate bacterial infections from viral infections and non-infectious inflammatory conditions. The evidence clearly demonstrates that:
- PCT concentration increases in bacterial infections but remains low in viral infections 1
- In a study of 360 children, PCT >1 μg/L had 83% sensitivity and 93% specificity for bacterial infection, while remaining low in viral infections 1
- PCT begins rising 4 hours after bacterial exposure, reaching maximum levels at 6-8 hours, and decreases rapidly after antibiotic treatment 2
Specific Evidence Regarding Herpes Viruses
The limited available evidence on herpes virus infections and procalcitonin supports that viral infections, including herpes viruses, do not significantly raise PCT:
- A case report of disseminated herpes simplex virus infection in a neonate showed a low procalcitonin level (1.6 ng/ml), which was inconsistent with bacteremia and suggested viral rather than bacterial etiology 3
- This low PCT level in severe herpes simplex infection strengthened the case for antiviral rather than antibacterial therapy 3
Clinical Application for Shingles
When evaluating a patient with shingles:
- Normal or minimally elevated PCT (<0.5 ng/mL) is expected with uncomplicated herpes zoster
- Significantly elevated PCT (>1 μg/L) should prompt investigation for bacterial superinfection, which is a recognized complication of shingles 4
- Bacterial superinfections can occur with herpes zoster, particularly in immunocompromised patients 5, 6
Important Caveats
If PCT is elevated in a patient with shingles, consider:
- Secondary bacterial superinfection of the vesicular lesions - this is the most common reason for PCT elevation in shingles patients
- Concurrent bacterial infection unrelated to the shingles
- Severe systemic inflammation in disseminated or complicated zoster (though this would still typically show lower PCT than bacterial sepsis)
Practical Algorithm
For a patient presenting with shingles and elevated inflammatory markers:
- PCT <0.5 ng/mL: Consistent with uncomplicated viral infection; no antibiotics needed
- PCT 0.5-1.0 ng/mL: Gray zone; assess clinically for bacterial superinfection of lesions
- PCT >1.0 ng/mL: High suspicion for bacterial superinfection or concurrent bacterial infection; consider antibiotics and search for bacterial source
The key distinction is that the viral reactivation of varicella-zoster virus itself does not trigger the procalcitonin response, making PCT a useful tool to identify when bacterial complications have developed in patients with shingles 1.