Primary antibody deficiency syndromes
| Primary antibody deficiency | Immunoglobulin levels |
| Common variable immune deficiency | Low IgG, low IgA, ± low IgM with a failure to mount a significant antibody response to vaccination.44 Usually identified in first 24 months of life |
| X-linked agammaglobulinaemia | Low IgG, low IgA, low IgM. Often occurs in boys before the age of 2 |
| IgG Subclass deficiencies | Low IgG subgroup 1–4 |
| Specific antibody deficiency | Normal serum levels of immunoglobulin but failure to respond to test immunisation |
| Selective IgA deficiency | Often symptom free. Estimated to affect 1:700 population45 |