What PCR test confirms Varicella-Zoster Virus (VZV) infection?

PCR Testing for Confirming Shingles (Varicella-Zoster Virus Infection)

Nucleic acid amplification technology (PCR) testing of material scraped or swabbed from skin lesions is the gold standard for confirming shingles, with sensitivity and specificity approaching 100%. 1

Diagnostic Approach for Shingles

Primary Diagnostic Test

• VZV PCR of lesion material:
  • Collect material by scraping or swabbing disrupted skin lesions 1
  • PCR can detect VZV DNA even in crusted lesions that are no longer considered infectious 1
  • Sensitivity and specificity both approach 100% 2
  • Can detect VZV DNA from various sources:
    • Vesicle fluid swabs
    • Skin scrapings
    • Crusts
    • Tzanck smear debris 3

Alternative or Complementary Testing

• For zoster sine herpete (shingles without visible rash):

  • VZV DNA PCR analysis of intact skin scrapings from the affected dermatome can confirm diagnosis 4

• CSF testing (if neurological involvement is suspected):

  • PCR testing of CSF for VZV DNA 1
  • Consider complementary CSF IgG and IgM testing for VZV when clinical suspicion is high, as PCR sensitivity from CSF can be notably low 2

Tests NOT Recommended for Diagnosis

• Serology (blood tests for VZV antibodies):
  • Not useful for diagnosis of chickenpox or shingles 1
  • VZV IgM antibody testing has limited utility, with positive results only appearing in 37% of confirmed cases 5
  • Even when positive, VZV IgM is only detectable for approximately 3.5 weeks after onset of symptoms 5

Comparison of Diagnostic Methods

Method	Sensitivity	Specificity	Notes
PCR of lesion material	~95-99%	~99%	Gold standard [2]
Direct immunofluorescent VZV antigen staining	82%	76%	Less sensitive and specific than PCR [6]
Virus culture	20%	100%	Very low sensitivity [6]
Serology (IgM/IgA)	48%	Variable	Only useful within 4 days of rash onset [6]
Tzanck smear	Variable	Low	Cannot differentiate between VZV and HSV [1]

Important Clinical Considerations

• PCR testing should be performed as early as possible in the disease course for optimal results
• Older diagnostic technologies (rapid antigen detection, Tzanck smear, electron microscopy) are more reliant on sample quality and timing, and have lower sensitivity 1
• PCR can detect VZV DNA from multiple specimen types, but vesicle fluid and skin scrapings provide slightly better detection rates than fixed tissue specimens 3
• For suspected cases without typical rash (zoster sine herpete), PCR of skin scrapings from the affected dermatome can still confirm diagnosis 4
• Prompt diagnosis is crucial for timely initiation of antiviral therapy, which can minimize the duration and severity of pain 4

By using PCR testing of lesion material as the primary diagnostic approach, clinicians can achieve rapid and accurate confirmation of VZV infection, allowing for appropriate treatment decisions and patient management.