Severe combined immunodeficiency

Last reviewed: 25 Aug 2022
Last updated: 15 Jan 2020



History and exam

Key diagnostic factors

  • presence of risk factors
  • recurrent and unusually severe infections
  • chronic diarrhoea
  • failure to thrive
  • absent lymphoid tissue
More key diagnostic factors

Other diagnostic factors

  • rash
  • oral or genital ulcers
  • microcephaly
  • skeletal abnormalities
  • blindness
  • dystonia
  • radiation sensitivity
Other diagnostic factors

Risk factors

  • Family history of SCID
  • Family history of infant death
  • Athabascan-speaking Native American people
  • Consanguinity
More risk factors

Diagnostic investigations

1st investigations to order

  • FBC
  • flow cytometry
  • chest x-ray
  • quantitative immunoglobulin test (IgG, IgM, and IgA)
More 1st investigations to order

Investigations to consider

  • T-cell proliferation studies
  • enzyme testing
  • serum uric acid
  • MRI chest
  • chest ultrasound
  • CT scan of the chest
  • genetic testing
  • radiation sensitivity of fibroblast cultures
  • polymerase chain reaction-based viraemia testing
  • fundoscopy
More investigations to consider

Treatment algorithm


confirmed SCID



Javier Chinen, MD, PhD

Associate Professor

Pediatrics, Allergy, and Immunology

Baylor College of Medicine

Texas Children’s Hospital




JC declares that he has no competing interests.


Dr Chinen would like to gratefully acknowledge Dr John M. Cunningham, Dr James L. LaBelle, Dr John Routes, Dr James Verbsky, Dr Nicole Chase, and Dr Ebrahim Shakir, the previous contributors to this topic. JLL, JR, JV, and NC are authors of references cited in this topic. JMC and ES declare that they have no competing interests.

Peer reviewers

Kathleen Sullivan, MD, PhD (CHOP)

Professor of Pediatrics

University of Pennsylvania


Division of Allergy and Immunology

Children's Hospital of Philadelphia




KS declares that she has no competing interests.

Charles Kirkpatrick, MD (UCHSC)

Professor of Medicine


Adult Immunodeficiency Program

University of Colorado Denver




CK is an author of a reference cited in this topic. CK has received speaker fees from Cention, Aventis Behring, and Bristol Myers Squibb. CK has received honorarium for speaking at the Aspen Allergy Conference, for the Colorado Allergy Society. CK ran the research program for a biotechnology company with an approximate budget of $3.5 million.

Waseem Qasim, BMedSci (Hons), MBBS, MRCP (UK), MRCPCH, PhD

Senior Lecturer

Institute of Child Health

Consultant in Paediatric Immunology & Bone Marrow Transplantation

Great Ormond Street Hospital




WQ declares that he has no competing interests.

  • Severe combined immunodeficiency images
  • Differentials

    • 22q11.2 Microdeletion syndrome/DiGeorge syndrome
    • Omenn's syndrome
    • Zeta chain-associated protein 70 deficiency
    More Differentials
  • Guidelines

    • Strimvelis for treating adenosine deaminase deficiency-severe combined immunodeficiency
    • Recommendations for screening and management of late effects in patients with severe combined immunodeficiency after allogenic hematopoietic cell transplantation
    More Guidelines
  • padlock-lockedLog in or subscribe to access all of BMJ Best Practice

Use of this content is subject to our disclaimer