Synopsis
Recognise infection patterns and immune dysregulation that exceed normal childhood illness, choose an age-aware first-line immune screen and protect infants with possible severe combined immunodeficiency while definitive testing proceeds.
- Count infection severity, site, organism, complications, treatment response and wellness between episodes; the pattern matters more than the raw number of colds.
- Normal nursery children can have frequent viral upper respiratory infections, but opportunistic organisms, invasive disease, repeated pneumonia, poor growth and incomplete recovery are not normal.
- A very low absolute lymphocyte count in an unwell infant is an emergency clue to severe combined immunodeficiency even when total white count appears normal.
- First-line tests are FBC with differential and film, age-adjusted IgG, IgA and IgM, and HIV testing, with culture review and organ assessment from the phenotype.
- Add vaccine-specific antibody responses for suspected humoral disease, lymphocyte subsets for cellular disease, neutrophil oxidative burst for phagocyte disease and CH50 or AP50 for complement pathways.
- Interpret every immunoglobulin and lymphocyte result against age-specific ranges; normal infant physiology and maternal antibody can mislead adult-style interpretation.
- Before immunology advice in suspected SCID, avoid live vaccines and ensure any required blood components follow the specialist irradiated and CMV-safe policy.
- Treat acute infection promptly and obtain microbiological diagnosis aggressively because usual inflammatory signs may be muted.
- Definitive management can include antimicrobial prophylaxis, immunoglobulin replacement, targeted immune therapy, haematopoietic stem-cell transplant or gene therapy.
- Test family members and provide genetic counselling when a molecular diagnosis changes recurrence, donor selection or early testing in future pregnancies.
Key red flags
Persistent or recurrent Pneumocystis, invasive fungal, disseminated mycobacterial, unusual viral or other opportunistic infection strongly suggests major T-cell dysfunction.
Failure to thrive with chronic diarrhoea, persistent thrush, recurrent pneumonia or an unexpectedly low absolute lymphocyte count in infancy requires urgent immunology assessment.
Deep abscesses, invasive bacterial infection, poor wound healing or absent pus suggests phagocyte number or function disorder.
Recurrent meningococcal or invasive encapsulated bacterial infection raises complement, antibody, asplenia or innate immune defects.
Family history of early male deaths, consanguinity, known immune disorder or severe vaccine complication materially lowers the threshold for urgent testing.
Autoimmune cytopenia, enteropathy, eczema, lymphoproliferation or granulomatous inflammation can be immune deficiency even when recurrent infection is not dominant.
Investigation priorities
Quantify absolute lymphocytes, neutrophils and platelets and identify morphology suggesting marrow or immune disease.
Management branches
An infant has opportunistic infection, severe thrush, diarrhoea, poor growth or lymphopenia.
- Admit, treat infection and contact paediatric immunology urgently without waiting for all screening results.
- Avoid live vaccines and use specialist-directed irradiated and CMV-safe blood components if required.
- Obtain lymphocyte subsets, HIV and pathogen testing while planning definitive molecular and transplant assessment.