Impact of Endogenous IgG Levels on Immunoglobulin Replacement Efficiency in Primary Immunodeficiency (PID)
Sunday, March 6, 2016: 4:45 PM
Concourse Foyer (Convention Center)
Stephen R. Jolles, MD PhD, Mark J Ponsford, John-Philip Lawo, PhD, Mikhail Rojavin, PhD
Rationale: Endogenous serum immunoglobulin G (IgGendo) levels at the time of primary immunodeficiency (PID) diagnosis vary widely from 0 to within the normal range. While there is no universal protective IgG level for all patients with PID, the initial target levels of IgG replacement therapy are usually low- to mid-normal range (7–10 g/L). IgG doses are then further adjusted to limit the infection burden as much as possible. Current dosing recommendations do not take into account IgGendo. It is not clear if this variable impacts the efficiency of IgG use.

Methods: Efficiency Index (EI) is introduced as a measure of how efficiently the exogenous IgG is used by each individual patient. EI was calculated as the difference between IgG trough level at steady state dosing and IgGendo at the time of diagnosis in g/L, divided by 4-weekly IgG dose in g/kg. Individual EI values were plotted vs. IgGendodata, including linear regression and a 95% confidence band.

Results: Pooled data from 110 PID patients from a single UK center with diagnoses of common variable immune deficiency, hypogammaglobulinemia, X-linked agammaglobulinemia, or specific antibody deficiency, treated with intravenous or subcutaneous IgG, were analyzed. EI was inversely proportional to IgGendo levels at diagnosis (R² = 0.1407). These results suggest that PID patients with lower IgGendo levels can utilize the same doses of IgG during replacement therapy more efficiently than patients with higher IgGendo levels.

Conclusions: Lower pre-treatment IgGendo levels in patients with PID correlate with higher efficiency of IgG replacement therapy.