Paeds · allergy-and-immunology
Primary immunodeficiency: warning signs and diagnostic approach
Also known as Inborn errors of immunity · Primary immunodeficiency disease · Recurrent infection workup · Jeffrey Modell warning signs · PID screening
Fellowship topic on primary immunodeficiency (inborn errors of immunity) in children: the Jeffrey Modell ten warning signs as the screening tool that turns 'just recurrent infections' into a referral; the modern IUIS 2022 classification spanning cellular-humoral, syndromic, antibody, immune-dysregulation, phagocyte, innate, autoinflammatory, complement, bone-marrow-failure and phenocopy categories; the pathophysiological logic that maps each immune arm to a characteristic infection signature — T-cell deficiency to opportunistic and viral or fungal infection, antibody deficiency to recurrent sinopulmonary infection with encapsulated bacteria, phagocyte defects to catalase-positive abscesses, and complement deficiency to neisserial sepsis; the tiered diagnostic protocol of screening immunoglobulins and full blood count with differential, escalating to lymphocyte-subset flow cytometry, vaccine-antibody response, CH50/AP50, neutrophil-function testing, TREC/KREC and genetic sequencing; the time-critical SCID prototype where lymphopenia and failure to thrive demand same-day immunology referral and a move to haematopoietic stem cell transplant before infection; the regional realities of newborn SCID screening by TREC; and the management stance of immunoglobulin replacement, infection prophylaxis, vaccination strategy, genetic counselling and the avoidance of live vaccines until cleared.
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Target exams
Red flags
- An infant with lymphopenia, failure to thrive and persistent or opportunistic infection — SCID until proven otherwise; same-day immunology referral and flow cytometry, because transplant before three to four months of age transforms survival
- A newborn screening result showing low or absent T-cell receptor excision circles (TRECs) — possible T-cell lymphopenia including SCID; urgent recall, confirm with flow cytometry, keep on prophylaxis, avoid live vaccines and breast-feed only if CMV-negative
- Two or more invasive bacterial infections, two or more months of oral antibiotics with no effect, or the need for intravenous antibiotics to clear infection — these are Jeffrey Modell warning signs that demand a primary immunodeficiency workup, not another antibiotic course
- Recurrent or severe Neisseria infection, or recurrent deep abscesses with catalase-positive organisms such as Staphylococcus aureus, Burkholderia or Serratia — pattern infection pointing to complement or phagocyte deficiency
- A family history of early childhood death from infection, consanguinity, or a known primary immunodeficiency — the pedigree is itself a warning sign and warrants testing even before symptoms
Life stages
Care settings
Clinical exam formats
Board mappings
- General Paediatrics and Allergy / Immunology: the Jeffrey Modell ten warning signs and the tiered diagnostic approach to primary immunodeficiency
- Recognise the SCID alarm — lymphopenia and failure to thrive in an infant is severe combined immunodeficiency until proven otherwise
- Renewed curriculum — Immunology (LG): IUIS 2022 classification of inborn errors of immunity and the immune-arm infection signatures
- Diagnostic pathway: screening immunoglobulins and FBC, lymphocyte subsets, vaccine response, complement, neutrophil function and genetic testing
- General Paediatrics: apply the warning signs in the recurrently unwell child and order the first-line tests correctly
- Urgent escalation: the abnormal newborn screening TREC result and the suspected SCID infant
- Long Case / Structured discussion: the child referred for recurrent infection — diagnostic workup, classification and shared decision-making
- Communication station: explaining a primary immunodeficiency diagnosis, immunoglobulin replacement and genetic counselling to a family
- Level 2 / 3 — Immunology & Infectious Disease: primary immunodeficiency recognition, the tiered diagnostic protocol and newborn SCID screening
- Patient safety and quality: the avoidable harm of diagnostic delay and the live-vaccine contraindication until cleared by immunology
- Foundation of Practice (FOP): warning signs, screening tests and the classification of primary immunodeficiency
- Applied Knowledge in Practice (AKP): TREC/KREC newborn screening, lymphocyte-subset interpretation and the SCID transplant window
- History-taking and management: the child with recurrent infection and the structured immunology workup
- Communication: explaining the diagnosis, treatment and inheritance to a family and planning school and transition care
- General Pediatrics Content Outline — primary immunodeficiency: warning signs and diagnostic approach
- Allergy & Immunology: IUIS classification, immune-arm infection signatures and the tiered laboratory workup
- Infectious Disease and Genetics: SCID as a time-critical diagnosis and the role of newborn screening
- Patient Care: recognise primary immunodeficiency through pattern infection and initiate the tiered workup and timely referral
- Systems-Based Practice: newborn screening programmes, immunoglobulin access and the multidisciplinary immunology service
- Medical Knowledge: IUIS 2022 classification, pathophysiology by immune arm and the diagnostic ladder
- Medical Expert: warning signs, diagnostic tiering and the interpretation of immunological investigations
- Health Advocate: equitable access to newborn screening, immunoglobulin and genetic services
- Communicator: explaining inheritance, treatment and the live-vaccine contraindication to families
The same clinic, two children
The child you can reassure
The child you must not miss
Overview & Definition
Picture an eight-month-old boy brought to clinic because he is not growing, has had two pneumonias in three months needing intravenous antibiotics, and has persistent oral thrush that will not clear. His full blood count shows a lymphocyte count that is low for his age. A cousin on the father's side died in infancy of an infection the family never understood. That cluster — failure to thrive, persistent opportunistic mucosal infection, recurrent deep infection needing intravenous antibiotics, lymphopenia, and a family history of early childhood death — is the signature that should make a clinician stop treating infection after infection and ask whether the child has a primary immunodeficiency. [1] [5]
Primary immunodeficiency is the older name for what the field now calls inborn errors of immunity: inherited disorders in which a defect in the development, function or regulation of the immune system produces a characteristic susceptibility to infection, immune dysregulation, autoimmunity, malignancy or a syndromic phenotype. They are not one disease but a large and growing family — the 2022 International Union of Immunological Societies classification lists nearly five hundred distinct conditions across ten categories — and the clinical challenge is that most children who present with recurrent infection do not have one. The skill the fellowship examiner is testing is the judgement to distinguish ordinary, exposure-driven childhood infection from the pattern that crosses into an immune-deficiency signature, and to act on that judgement with a tiered workup rather than another antibiotic course. [2] [3]
References12ShowHide
- [1]Subbarayan A; Colarusso G; Hughes SM; Gennery AR; Slatter M; Cant AJ; Barge D; Flood T; Abinun M; Hambleton S Clinical features that identify children with primary immunodeficiency diseases. Pediatrics, 2011.PMID 21482601
- [2]Tangye SG; Al-Herz W; Bousfiha A; Chatila T; Cunningham-Rundles C; Etzioni A; et al Human Inborn Errors of Immunity: 2022 Update on the Classification from the International Union of Immunological Societies Expert Committee. J Clin Immunol, 2022.PMID 35748970
- [3]Bousfiha A; Moundir A; Tangye SG; Picard C; Ochs HD; Casanova JL; et al The 2022 Update of IUIS Phenotypical Classification for Human Inborn Errors of Immunity. J Clin Immunol, 2022.PMID 36198931
- [4]Bousfiha A; Jeddane L; Picard C; Ailal F; Bobby Gaspar H; Al-Herz W; et al Human Inborn Errors of Immunity: 2019 Update of the IUIS Phenotypical Classification. J Clin Immunol, 2020.PMID 32048120
- [5]de Vries E; European Society for Immunodeficiencies (ESID) members Patient-centred screening for primary immunodeficiency, a multi-stage diagnostic protocol designed for non-immunologists: 2011 update. Clin Exp Immunol, 2012.PMID 22132890
- [6]Kwan A; Abraham RS; Currier R; Brower A; Andruszewski K; Fuller TM; et al Newborn screening for severe combined immunodeficiency in 11 screening programs in the United States. JAMA, 2014.PMID 25138334
- [7]Fried AJ; Bonilla FA Pathogenesis, diagnosis, and management of primary antibody deficiencies and infections. Clin Microbiol Rev, 2009.PMID 19597006
- [8]Seidel MG; Kindle G; Gathmann B; Quinti I; Buckland M; van Montfrans J; et al The European Society for Immunodeficiencies (ESID) Registry Working Definitions for the Clinical Diagnosis of Inborn Errors of Immunity. J Allergy Clin Immunol Pract, 2019.PMID 30776527
- [9]Kwan A; Puck JM History and current status of newborn screening for severe combined immunodeficiency. Semin Perinatol, 2015.PMID 25937517
- [10]Kobrynski L; Powell RW; Bowen S Prevalence and morbidity of primary immunodeficiency diseases, United States 2001-2007. J Clin Immunol, 2014.PMID 25257253
- [11]Thakar MS; Logan BR; Puck JM; Pai SY; Notarangelo LD; Satter LF; et al Measuring the effect of newborn screening on survival after haematopoietic cell transplantation for severe combined immunodeficiency: a 36-year longitudinal data linkage study. Lancet, 2023.PMID 37352885
- [12]Amatuni GS; Currier RJ; Church JA; Lin P; McGhee SA; Murrell K; et al Newborn Screening for Severe Combined Immunodeficiency and T-cell Lymphopenia in California, 2010-2017. Pediatrics, 2019.PMID 30683812