Do Not Treat with IVIG
A patient with an IgG level of 324 mg/dL who has not been ill does not meet criteria for IVIG therapy and should not be treated. 1
Diagnostic Criteria Not Met
The absence of recurrent infections is the critical factor here. Treatment guidelines are clear and consistent:
- IVIG is indicated only when BOTH hypogammaglobulinemia AND recurrent infections are present - specifically defined as IgG <400-500 mg/dL with at least 3 infections per year. 1
- The American Academy of Allergy, Asthma, and Immunology explicitly requires documented recurrent infections alongside low IgG levels before initiating replacement therapy. 1
- Simply having a low IgG number without clinical manifestations (infections) does not justify treatment. 2
What You Should Do Instead
Evaluate functional antibody production before making any treatment decisions:
- Measure specific antibody responses to pneumococcal vaccines (both polysaccharide and conjugate vaccines) to assess whether the patient can mount protective responses despite the low total IgG. 1
- Enumerate lymphocyte subsets by flow cytometry, particularly CD19+ B cells and memory B-cell populations. 1
- Review medication history thoroughly - drugs like phenytoin, carbamazepine, valproic acid, sulfasalazine, hydroxychloroquine, and NSAIDs can cause acquired hypogammaglobulinemia that reverses with drug cessation. 2
Monitoring Strategy
Close observation with serial measurements is the appropriate approach:
- Repeat IgG measurement in 1-3 months to confirm the low level is persistent, not transient. 2
- Document infection history prospectively - track any sinopulmonary infections, pneumonias, or other bacterial infections over the next 6-12 months. 1
- If the patient develops recurrent infections (≥3 per year) or severe infections requiring hospitalization, then reassess for IVIG initiation. 1
Common Pitfall to Avoid
Do not treat laboratory values in isolation. Approximately 2.5% of the normal population will have IgG levels below the reference range by statistical definition, and many remain healthy without infections. 2 The decision to initiate expensive, lifelong therapy with potential adverse effects (including anaphylaxis risk, thromboembolism, renal failure, and aseptic meningitis) must be based on clinical disease, not just a number. 3
If this patient later develops recurrent infections, the standard IVIG dosing would be 0.2-0.4 g/kg every 3-4 weeks, targeting trough IgG levels of 600-800 mg/dL. 1