Laboratory Testing for Shingles
In immunocompetent patients with typical presentation, laboratory testing is not required—clinical diagnosis is sufficient. 1, 2
When Laboratory Testing IS Needed
Laboratory confirmation should be obtained in the following situations:
- Immunocompromised patients (including HIV infection, transplant recipients, those on immunosuppressive therapy) 1, 2
- Atypical clinical presentations where the diagnosis is uncertain 1, 2
- Cases where clinical features overlap with other conditions (such as herpes simplex virus infection) 2
Recommended Laboratory Test
PCR testing of vesicle fluid is the gold standard with nearly 100% sensitivity and specificity for detecting varicella-zoster virus DNA. 1, 2
Specimen Collection Technique
- Collect material from the base of unroofed vesicles by scraping or swabbing disrupted skin lesions 2
- Sample early in the disease course when vesicles are present for highest diagnostic yield 2
- Place specimens in appropriate transport medium immediately after collection 2
- PCR can detect VZV DNA even in crusted lesions that are no longer infectious 2
Tests That Are NOT Useful
- Serology (VZV IgG/IgM) should NOT be used for diagnosis of active shingles—it is only useful for determining immunity status, not for diagnosing acute infection 2
- Tzanck smear (microscopy) cannot differentiate between VZV and HSV infections and requires a skilled microscopist 2
Clinical Context
For typical immunocompetent patients presenting with unilateral dermatomal vesicular rash that respects the midline, start treatment immediately based on clinical diagnosis alone without waiting for laboratory confirmation. 1 The prodromal pain typically precedes the rash by 24-72 hours, and lesions progress from erythematous macules to vesicles that crust over within 4-6 days. 1
Laboratory confirmation becomes particularly important when clinical diagnosis alone could lead to false positive or false negative diagnoses, especially in immunocompromised hosts where presentation may be atypical. 2