Correlation of IgG Levels and Frequency of Infections in Antibody-Deficiency Patients

Introduction/Background Patients with antibody deficiency commonly receive immunoglobulin replacement therapy (IgRT), but markers for disease control vary. The normal range for IgG ranges from 600 to 1700 mg/dL, with providers commonly aiming for a lower threshold of at least 550 mg/dL in these patients. A case series of two patients suggested that levels >800 mg/dL could provide significantly increased protection against infection and advocated tailoring IgRT doses based on specific patient outcomes (1). Methods Data collection was completed for 75 antibody-deficiency patients receiving subcutaneous immunoglobulin (SCIG) or intravenous immunoglobulin (IVIG). Of 75 patients, 13 were adults and all had CVID. Among pediatric patients, 55 had primary immunodeficiencies (PID): 9 CVID, 29 hypogammaglobulinemia, 7 Bruton’s agammaglobulinemia, 3 STAT-1 gain-of-function (GOF) mutation, 3 autoimmune lymphoproliferative syndrome (ALPS), and 4 specific antibody deficiency (SAD) with normal immunoglobulins and B cells. Seven remaining pediatric patients had secondary immunodeficiencies (SID) caused by end-stage renal disease or lymphoma. Data were annualized and patients were divided into “well-controlled” and “uncontrolled” disease. Lack of disease control was defined as greater than three courses of oral antibiotics or steroids yearly and >1 ED/ICU admission annually. Data/Results On average, well-controlled patients had three to four infections per year, while uncontrolled patients had six despite consistent IgRT treatment. The upper limit of IgG levels for any patient in this study did not exceed 1,394 mg/dL. The calculated average steady state IgG levels across the key subgroups are as follows: Well-controlled CVID: 844 mg/dL Well-controlled hypogammaglobulinemia: 899 mg/dL Suboptimally-controlled CVID: 635 mg/dL Suboptimally-controlled hypogammaglobulinemia: 606 mg/dL Bruton’s patients had no fewer than 4 infections annually, and an average IgG level of 637 mg/dL. Patients with SAD and ALPS had better disease control with an average steady-state IgG of 1,012 mg/dL. Patients with STAT-1 GOF had the highest steady-state IgG levels (988 mg/dL). In SID, IgG levels were difficult to capture due to inconsistent therapy use. There was no statistically significant difference between the adult and pediatric cohorts. Conclusion These results indicate the optimal IgG level for treatment should change based on diagnosis, but likely begins at least 800 mg/dL.