Diagnostic Approach to Humoral Immunodeficiencies

Introduction to Humoral Immunodeficiency Diagnosis

The American Academy of Allergy, Asthma, and Immunology recommends the use of protein electrophoresis with measurement of gammaglobulins to diagnose humoral immunodeficiencies, primarily common variable immunodeficiency (CVID), agammaglobulinemia, selective IgA deficiency, and IgG subclass deficiencies 1, 2

Agammaglobulinemia is characterized by the absence or extremely low levels of all immunoglobulins (IgG, IgA, IgM) with absent or severely reduced B cells (<2% of lymphocytes), according to the Journal of Allergy and Clinical Immunology 1, 2
The X-linked form (Bruton's disease) accounts for 85% of cases, as stated by the Journal of Allergy and Clinical Immunology 3
Typical presentation occurs in the first 2 years of life with recurrent bacterial respiratory infections, as noted by the Journal of Allergy and Clinical Immunology 4
Common Variable Immunodeficiency (CVID) is characterized by IgG <450-500 mg/dL plus IgA or IgM below the 5th percentile, with defective specific antibody production, as defined by the Journal of Allergy and Clinical Immunology 5, 6
B cells are normal or moderately reduced (approximately 13% of patients have <3% B cells) in CVID, according to the Journal of Allergy and Clinical Immunology 1, 6
CVID should not be diagnosed before the age of 4 years, as stated by the Journal of Allergy and Clinical Immunology 1, 6
Selective IgA deficiency is characterized by IgA <7 mg/dL with normal IgG and IgM in patients over 4 years old, as defined by the Journal of Allergy and Clinical Immunology 1, 4
It is the most common primary immunodeficiency, affecting approximately 1 in 300-700 individuals of white race, as noted by the Journal of Allergy and Clinical Immunology 4

Measuring albumin and total serum protein simultaneously is crucial to distinguish protein-losing conditions from production defects, as recommended by the Journal of Allergy and Clinical Immunology 5, 4
Primary immunodeficiencies typically have normal albumin and total protein because only immunoglobulin production is affected, as stated by the Journal of Allergy and Clinical Immunology 5

Initial studies with protein electrophoresis should include quantitative measurement of immunoglobulins (IgG, IgA, IgM) and possibly IgG subclasses, as recommended by the Journal of Allergy and Clinical Immunology 1, 2
Total protein and albumin should be measured to distinguish protein loss from production defects, as noted by the Journal of Allergy and Clinical Immunology 5, 4
Functional studies, including specific antibody responses to protein and polysaccharide antigens (vaccines), are essential to document functional antibody deficiency, as stated by the Journal of Allergy and Clinical Immunology 1, 5, 6
Enumeration of B cells by flow cytometry is essential to distinguish CVID (normal/reduced B cells) from agammaglobulinemia (absent B cells), as recommended by the Journal of Allergy and Clinical Immunology 5, 6

Patients with IgG <300-400 mg/dL are at severe risk of potentially life-threatening bacterial infections, particularly from encapsulated organisms (Streptococcus pneumoniae, Haemophilus influenzae), as noted by the Journal of Allergy and Clinical Immunology 5, 4
Recurrent respiratory infections are the characteristic presentation, as stated by the Journal of Allergy and Clinical Immunology 4
Urgent indication for immunoglobulin replacement therapy should be considered for patients with IgG <300 mg/dL to reduce the risk of potentially life-threatening infections, as recommended by the Journal of Allergy and Clinical Immunology 5
Treatment criteria include initiating therapy for patients with ≥2 severe recurrent infections from encapsulated bacteria, regardless of the exact IgG level, as noted by the Journal of Allergy and Clinical Immunology 4
Standard dose is IGIV 0.2-0.4 g/kg every 3-4 weeks, with target IgG levels of 8-11 g/L, as recommended by the Journal of Allergy and Clinical Immunology 5, 6
Monitoring should focus on the frequency of infections rather than serum levels alone to evaluate clinical response, as stated by the Journal of Allergy and Clinical Immunology 5, 4

Failing to measure albumin and total protein can lead to misdiagnosis of protein-losing syndromes as primary immunodeficiency, as noted by the Journal of Allergy and Clinical Immunology 4
Inadequate medication history can miss reversible drug-induced hypogammaglobulinemia, as stated by the Journal of Allergy and Clinical Immunology 4
Premature diagnosis of CVID before the age of 4 years can lead to misdiagnosis, as CVID should not be diagnosed before this age, according to the Journal of Allergy and Clinical Immunology 1, 6