Synopsis
Recognise clinically important immune failure, distinguish inherited from acquired causes, map infection patterns to immune compartments and investigate urgently without delaying treatment of active infection.
- Suspect immunodeficiency when infections are unusually severe, persistent, recurrent, treatment-resistant or caused by unusual organisms, rather than counting minor infections alone.
- Primary immune regulatory disorders can present from infancy to adulthood and may cause autoimmunity, inflammation, lymphoproliferation or malignancy as well as infection.
- Secondary causes are more common: medicines, haematological malignancy, HIV, protein loss, malnutrition, asplenia, renal disease and critical illness can impair different compartments.
Key red flags
Invasive infection, repeated hospitalisation, failure of standard treatment, opportunistic organisms or infection at multiple sites raises concern beyond ordinary frequency.
Thrush, chronic diarrhoea, failure to thrive, persistent viral infection or vaccine-strain disease in infancy demands urgent specialist assessment.
Reasoning priorities
Retrieve organisms, culture sites, imaging, antimicrobial courses, severity and response across records.
Repeated viral upper-respiratory symptoms differ from culture-proven pneumonia, opportunistic infection or invasive encapsulated bacterial disease.
Worked reasoning
A 38-year-old has three radiologically confirmed pneumonias in two years, chronic sinusitis and low globulin; there is no known childhood diagnosis.
- Assess current infection severity and treat promptly, while building a verified timeline of organisms, sites, imaging, antibiotic response and structural lung damage.
- Recognise an antibody-pattern phenotype that can present in adulthood, but review secondary causes including B-cell-active medicines, haematological disease, HIV risk and protein loss.
- Order initial full blood count with film, quantitative immunoglobulins, renal and liver profiles, albumin and consented HIV testing, and discuss early with clinical immunology before unstructured panels.
- Verify abnormalities when clinically appropriate, arrange specialist functional testing and pulmonary assessment, and base prophylaxis or replacement on diagnosis and infection outcomes rather than one concentration.