Pediatric Chickenpox Workup

Updated: Aug 24, 2021
  • Author: Kirsten A Bechtel, MD; Chief Editor: Russell W Steele, MD  more...
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Approach Considerations

In general, laboratory studies are unnecessary for diagnosis, because varicella is clinically obvious. However, some tests and procedures may be helpful in confirming the diagnosis or identifying complications. Imaging studies are typically not required for varicella unless secondary complications are a concern (eg, chest radiography for varicella pneumonia).

Go to Chickenpox for complete nonpediatric information on this topic.


Blood Studies

White blood cell count

Most children with varicella have leukopenia in the first 3 days, followed by leukocytosis. Marked leukocytosis may indicate a secondary bacterial infection but is not a dependable sign. Most children with significant secondary bacterial infections do not have leukocytosis; neutrophilic leukocytosis and neutrophilia occur in only a few cases involving serious bacterial infections. Investigations cannot be relied on to diagnose or exclude bacterial infection.

Alanine aminotransferase level

Significant elevations of alanine aminotransferase (ALT) occur in 20-50% of children and adolescents with varicella complicated by hepatitis, but elevations return to normal within one month in almost all cases.


Staining and Other Tests

Tzanck smear

A Tzanck smear involves scraping the base of the lesions and then staining the scrapings to demonstrate multinucleated giant cells. The presence of multinucleated giant cells suggests a herpes virus infection but is not specific for varicella-zoster virus. Infections with other herpes viruses, such as herpesvirus 1 and 2, also display similar multinucleated giant cells. Thus, this finding is not sufficiently sensitive or specific for varicella and should be replaced by the more specific immunohistochemical staining of such scrapings, if available.

Immunohistochemical staining

Immunohistochemical staining of skin lesion scrapings can confirm varicella. The procedure is useful for high-risk patients who require rapid confirmation.

Polymerase chain reaction

Polymerase chain reaction (PCR) examination of skin scrapings is quick and sensitive. This test is replacing other methods as the equipment becomes more widely available.


Bacterial culture of lesions may be indicated if signs of superinfection are present.



Serologic Studies

Serology is mainly used to confirm past infection to assess a patient’s susceptibility status. This helps determine preventive treatment requirements for an adolescent or adult who has been exposed to varicella.

Among the many serologic studies, the most sensitive are the indirect fluorescent antibody (IFA), fluorescent antibody to membrane antigen (FAMA), neutralization test (NT), and radioimmunoassay (RIA). These time-consuming tests require specialized equipment that renders them unsuitable for routine use.

Commercially available latex agglutination (LA) and enzyme-linked immunosorbent assay (ELISA) tests are sensitive and rapid. Although the complement fixation test is often used, its sensitivity is low.


Chest Radiography

Children with high temperatures and respiratory signs should have chest radiography to confirm or exclude pneumonia. Chest radiographic findings may be normal or may show diffuse bilateral nodular infiltrates in primary varicella pneumonia. Radiography may also detect focal infiltrates suggestive of secondary bacterial pneumonia.


Lumbar Puncture

Children with neurological signs should have their cerebrospinal fluid (CSF) examined. The CSF of patients with varicella encephalitis may have few or as many as 100 cells that are polymorphonuclear or mononuclear, depending on the timing of the lumbar puncture. Glucose levels are within the reference range. Protein levels are within the reference range or are slightly elevated.