What is the role of lab testing in the diagnosis of croup?

Updated: Oct 09, 2019
  • Author: Germaine L Defendi, MD, MS, FAAP; Chief Editor: Russell W Steele, MD  more...
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Laboratory test results rarely contribute to confirm diagnosis. The complete blood cell (CBC) count is usually nonspecific, although the white blood cell (WBC) count and differential may suggest a viral etiology with lymphocytosis. Identifying the specific viral etiology (eg, parainfluenza virus type) via nasal washings is typically not necessary, but may be useful to determine isolation needs in the hospital care setting or, in the case of influenza A, to decide whether antiviral therapy should be initiated.

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