Investigations
1st investigations to order
clinical diagnosis
Test
Clinical findings are usually sufficient to make a diagnosis.
Result
typical vesicular rash at different stages, with pruritus, fever, malaise, frequently a history of exposure
Investigations to consider
polymerase chain reaction
Test
Most sensitive and specific test for varicella-zoster virus.
Detects DNA in fluids and tissues.[67]
May not be available at all laboratories.
Result
positive for virus DNA
viral culture
Test
Positive in <50% of samples, but can help distinguish from other viral pathogens.[65] May take up to 21 days for positive result.
Result
positive varicella-zoster virus in culture
direct fluorescent antibody testing (DFA)
Test
More rapid results and more sensitive than viral culture.
Result
positive for varicella-zoster virus antigen (indicating that virus is present)
Tzanck smear
Test
Used less frequently for diagnosis, particularly since it is not as accurate as DFA and it is not specific for varicella-zoster virus.
Result
multi-nucleated giant cells under microscopic evaluation
latex agglutination (LA)
enzyme-linked immunosorbent assay (ELISA)
Test
Not useful in acute disease.
Similar to LA in terms of sensitivity, and can be used to test for immunity after exposure to the varicella-zoster virus or vaccine.[68]
Recommended in pregnant women who have possibly been exposed and have an unknown immune status.[50]
Result
positive for IgG for varicella
complement fixation
Test
Insensitive and may not be specific at low titres.
Recommended in pregnant women who have possibly been exposed and have an unknown immune status.[50]
Result
positive for IgG for varicella
ultrasound (pregnant women)
Test
Ultrasound is recommended for all women who develop varicella in pregnancy, to screen for fetal consequences of infection.[50]
Result
screening for fetal abnormalities
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