How is severe combined immunodeficiency (SCID) diagnosed?

Updated: Apr 28, 2021
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: Harumi Jyonouchi, MD  more...
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Lymphopenia is the classic hallmark of severe combined immunodeficiency (SCID); however, normal or even elevated lymphocyte counts can be seen in a significant proportion of patients. Failure to make the diagnosis because the child is not frankly lymphopenic may present a problem, particularly in patients with Omenn syndrome, bare lymphocyte syndrome, and interleukin (IL)–2 deficiency. Obtaining lymphocyte markers and test results of antibody and lymphocyte proliferation can help physicians to avoid this pitfall.

Other laboratory studies can be performed on the basis of clinical judgment, depending on the nature of the infection and the organ system involved. Specifically, assays that measure the ability of lymphocytes to respond to activating agents, such as pokeweed mitogen and phytohemagglutinin, are valuable. Imaging studies are not useful for diagnosis of the primary condition; however, obtaining a chest radiograph may be necessary to evaluate pneumonia secondary to SCID.

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