Suspected immunodeficiency in children

Paediatrics · Symptom or situation · updated 2026-10-30

BioMG follows French guidelines. Adapt it to the guidelines and the tests available where you practise.

Frequency: Inherited immunodeficiencies: about 1 birth in 2 000, i.e. approximately 400 new cases a year in France ^[1]

First-line tests

FBC (± blood film)
Serum immunoglobulins (IgG, IgA, IgM)
Vaccine serologies (DTP, Haemophilus, pneumococcus)
blood group isohaemagglutininsif neededChild over 24 months: explores production of anti-polysaccharide antibodies.
HIV serologyif neededTo rule out acquired immunodeficiency: the diagnosis of HIV infection should be considered at any age, even if the mother's serology was negative at the start of pregnancy.
CH50, total haemolytic complement (if personal or family meningococcal meningitis, or invasive infection with an encapsulated bacterium)if neededPersonal or family history of meningococcal meningitis: the PNDS lists complement investigation among the possible tests reimbursed in the community; for invasive infection with an encapsulated bacterium, it places it in the second-line tests ^[2]. In the United States, an American Family Physician review measures complement in the initial tests for any suspected immunodeficiency in a child: a normal CH50 rules out a significant deficiency, and the alternative pathway (AH50) is measured only if it is abnormal (expert opinion, 2013) ^[3]. In Australia, ASCIA (2025) screens for complement deficiency with C3, C4, CH50 and AH50 for bacterial infection, especially Neisseria, autoimmunity or recurrent angio-oedema ^[4].

Detailed explanation and international comparison (in French): read it in English (machine translation)

Serum protein electrophoresis: unhelpful in children for the diagnosis of hypogammaglobulinaemia, given the variations of IgG, IgA and IgM during childhood ^[2].
IgG measurement before 3 to 4 months: reflects maternal IgG and cannot be interpreted ^[2].
Multiplying vaccine serologies: tetanus, Haemophilus and pneumococcus are enough ^[2].
Isolated IgG4 measurement: an isolated IgG4 deficiency is not an immunodeficiency ^[5].

IgG subclass assay (IgG1, IgG2, IgG3, IgG4), after 18 to 24 months, in case of recurrent infections despite normal IgG
Blood group isohaemagglutinins
Blood film
Complement work-up (CH50)
Complement work-up (AP50)
Total IgE
T, B and NK lymphocyte phenotypingif neededSecond-line test of the PNDS in case of confirmed isolated lymphopenia, hypogammaglobulinaemia beyond 3 months, low or absent serology after a documented infection, or isolated defect of vaccine antibody production checked 4 to 6 weeks after a booster ^[2]; P. Frange proposes it if immunoglobulins, IgG subclasses or allohaemagglutinins are abnormal ^[5,6]. It is coded like the lymphocyte count by flow cytometry (CD3, CD4, CD8…), procedure 1122 ^[9]. The NABM names only the T lymphocyte subsets (procedure 1122): the coding of B and NK lymphocytes depends on the laboratory.

Detailed explanation and international comparison (in French): read it in English (machine translation)

Sources (10)