# Recognising Immunodeficiency in Children

> Immunodeficiency for FMGE Paediatrics: 10 warning signs, age and organism patterns, SCID emergency, Bruton, CGD, DiGeorge and IVIG.

- Canonical URL: https://prepelephant.com/topics/fmge/paediatrics/immunodeficiency-recognition-fmge
- Exam / course: FMGE · Subject: Paediatrics
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Recognising Immunodeficiency in Children", PrepElephant, https://prepelephant.com/topics/fmge/paediatrics/immunodeficiency-recognition-fmge

## Direct answer

Recurrent, deep, unusual or persistent infections — four pneumonias in a year, two deep abscesses, persistent oral thrush beyond infancy, disseminated BCG in an infant — should raise immunodeficiency above "just low immunity"; the Jeffrey Modell ten warning signs are the screening checklist. Secondary immunodeficiency (malnutrition, measles, HIV, steroids) outnumbers primary disease many times over in India, but primary disorders have a teachable logic by age and organism: antibody defects declare after maternal IgG wanes at four to six months with sinopulmonary and diarrhoeal infections; combined T-cell defects (SCID) present in the first months with opportunists — Pneumocystis, persistent candida, chronic diarrhoea, failure to thrive — and are killed by live vaccines; complement defects recur with Neisseria. A lymphocyte count low for age on an existing CBC is the free clue to SCID, a paediatric emergency.

## What you must remember

- **The 10 warning signs (Jeffrey Modell):** eight or more ear infections yearly, two or more serious sinusitis, two or more months of ineffective antibiotics, two or more pneumonias a year, failure to thrive with infection, recurrent deep abscesses, persistent thrush after one year, intravenous-antibiotic need, two or more deep-seated infections, and family history.
- **Age-of-onset logic:** opportunists and oral thrush from birth — combined T-cell (SCID); four to six months onwards with sinopulmonary infection — antibody deficiency (maternal IgG gone); later childhood to adolescence — common variable immunodeficiency, complement or specific antibody defects.
- **Bruton agammaglobulinaemia (X-linked):** boys after about six months, recurrent bacterial infection, absent tonsils and adenoids, absent B cells (CD19) with all immunoglobulin classes low; replacement immunoglobulin 400-600 mg/kg every three to four weeks.
- **SCID:** the emergency — chronic diarrhoea, Pneumocystis pneumonia, persistent candida, failure to thrive, lymphopenia for age, absent thymic shadow; live vaccines (BCG, OPV, rotavirus, measles) cause disseminated disease; management is cotrimoxazole prophylaxis, immunoglobulin, irradiated CMV-negative blood and stem-cell transplantation; ADA deficiency is the classic enzymatic type.
- **Syndromic patterns:** DiGeorge (22q11.2): CATCH-22 — cardiac defects, abnormal facies, thymic aplasia, cleft palate, hypocalcaemia — suspect in a neonate with hypocalcaemic convulsions and conotruncal heart disease. Wiskott-Aldrich: eczema, small-platelet thrombocytopenia and recurrent pyogenic infection in a boy.
- **Organism-specific defects:** chronic granulomatous disease — recurrent abscesses and granulomas with catalase-positive organisms (Staphylococcus aureus, Aspergillus, Serratia, Nocardia) including BCGitis, diagnosed by an absent nitroblue tetrazolium (or DHR) test; terminal complement (C5-C9) deficiency — recurrent meningococcal disease.
- **Workup ladder:** CBC with differential (lymphopenia or neutropenia for age), immunoglobulins, post-vaccination titres, lymphocyte subsets, HIV serology always, then targeted function tests (NBT, DHR, complement) with genetic confirmation.

## A seven-month-old who keeps failing

A seven-month-old of consanguineous parents has been admitted thrice: Pneumocystis pneumonia, oral candida resisting topical therapy, chronic diarrhoea with weight faltering — and the BCG scar is inflamed and draining. The assembly is diagnostic before any fancy test: opportunists plus persistent candida plus failure to thrive plus disseminated BCG in an infant means combined immunodeficiency. Notice the free clue — the old CBC shows a lymphocyte count of 1600, low for a seven-month-old (infants normally run 4000 or more). Act as an emergency: isolate, stop all live vaccines, start cotrimoxazole prophylaxis, replace immunoglobulin, use irradiated CMV-negative blood, and refer urgently for transplantation — survival falls with every infection accumulated while waiting. The counter-case: a toddler with six ear infections a year, normal growth and vaccine responses, has daycare exposure, not immunodeficiency.

## Where students slip

Sending every SCID stem to an HIV test alone is the classic miss — HIV is on the list, but BCGitis plus candida in an infant is combined immunodeficiency until proven otherwise, and consanguinity nudges toward primary disease. Second: in Bruton the tonsils are absent and CD19 counts near zero — a physical-sign-plus-lab pairing the exam loves. Third: organism specificities — catalase-positive organisms for CGD, Neisseria for complement, enterovirus and giardia for antibody defects, Pneumocystis and candida for T-cell defects. Fourth: an otherwise well child with anaphylactoid transfusion reactions needs IgA levels, not an allergy label.

## Frequently asked questions

### What are the Jeffrey Modell warning signs of primary immunodeficiency?

Eight-plus ear infections yearly, two-plus serious sinusitis, ineffective two-month antibiotic courses, two-plus pneumonias a year, failure to thrive with infection, deep abscesses, persistent thrush after one year, intravenous-antibiotic need, deep-seated infections, and family history.

### Which immunodeficiency presents in early infancy with opportunistic infection?

Severe combined immunodeficiency — Pneumocystis, persistent candida, chronic diarrhoea, failure to thrive, lymphopenia for age, absent thymic shadow — a transplant-track emergency in which live vaccines are lethal.

### Why does Bruton agammaglobulinaemia present after six months of age?

Passively transferred maternal IgG protects until it degrades over the first months of life; once gone, the boy with no B cells and near-absent tonsils develops recurrent bacterial sinopulmonary infection.

### Which organisms suggest chronic granulomatous disease?

Catalase-positive organisms — Staphylococcus aureus, Aspergillus, Serratia, Nocardia — including BCGitis, diagnosed by an absent nitroblue tetrazolium reduction.

### What screening tests start the immunodeficiency workup?

Complete blood count with differential for age-appropriate lymphocyte and neutrophil counts, quantitative immunoglobulins, post-vaccination antibody titres and HIV testing, escalating to lymphocyte subsets and functional assays.