Contents
Disorders in which part of the body’s immune system is missing or does not function normally due to a primary cause (usually genetic).

Classification
International Union of Immunological Societies:
Nine classes of primary immunodeficiencies:
- Combined T and B–cell immunodeficiencies
- Predominantly antibody deficiencies
- Other well-defined immunodeficiency syndromes
- Diseases of immune dysregulation
- Congenital defects of phagocyte number, function, or both
- Defects in innate immunity
- Autoinflammatory disorder
- Complement deficiencies
- Phenocopies of primary immune deficiencies

Diagnosis
European Society of Immunodeficiencies (ESID) warning signs for suspicion of PID:
- ≥ 4 new infections in a year
- ≥ 2 serious sinus infections in a year
- ≥ 2 cases of pneumonia in a year
- ≥ 2 months of antibiotics without effect
- Failure of an infant to gain weight or grow normally
- Recurrent deep skin infections or organ abscesses
- Persistent oral thrush, or candidiasis elsewhere beyond infancy
- Need for IV antibiotics to clear infections
- ≥ 2 deep-seated infections (e.g. meningitis, cellulitis)
- Family history of immunodeficiency
Screening investigations:
- Total and differential leukocyte counts, leukocyte morphology
- HN serology
- X-ray chest
- Delayed skin tests (Candida, tetanus toxoid)
Specific investigations:
- Blood levels of immunoglobulins: IgG, IgA, IgM; IgG subclasses
- Blood group isohemagglutinins (for functional IgM)
- Anti-diphtheria and anti-tetanus antibodies (functional IgG)
- Lymphocyte subsets: CD3, CD4, CD8, CD19, CD16
- Mitogen stimulation tests (response to phytohemagglutinin)
- Nitroblue tetrazolium (NBT) dye reduction test
- CHSO, complement component assays
- Mannan-binding lectin assay
- Enzyme assays: adenosine deaminase, purine nucleoside phosphorylase
- HLA typing
- Bacterial killing
- Chemiluminescence studies
Management
Haematopoietic stem cell transplantation (HSCT):
- Done in early infancy
- Cannot be carried out for children with ataxia-telangiectasia
Immunoglobulin therapy:
- Types:
- Intravenous (IVIg)
- Subcutaneous (ScIg)
- Intramuscular (IMIg)
- Composition: 90% monomeric IgG + IgA & IgM
- Dose: 0.4-0.6 g/kg every 3-4 weeks
- Complications:
- Short-term: Anaphylaxis, chills or rigors
- Long-term: Hepatitis C infection