Your Main Immune Memory Antibody
IgG is the most abundant antibody in your blood—it's the backbone of your adaptive immune defense. IgG represents your immune memory: past infections you've fought, vaccines you've received. It crosses the placenta to protect newborns. Low IgG means your immune memory bank is depleted.
What is IgG (Immunoglobulin G)?
IgG is the most abundant immunoglobulin (~75% of serum Ig). Four subclasses: IgG1 (65%), IgG2 (25%), IgG3 (7%), IgG4 (3%). Provides long-term immunity, opsonization, complement activation, and neutralization. Half-life ~21 days. Crosses placenta.
↑ What High IgG (Immunoglobulin G) Means
Chronic infections, autoimmune disease, chronic liver disease, or IgG-producing multiple myeloma (IgG subtype). Polyclonal elevation (all subtypes up) = reactive/inflammatory. Monoclonal spike (one sharp band) = concerning for myeloma or MGUS.
Common symptoms:
If polyclonal: symptoms of underlying infection/inflammation · If monoclonal: bone pain, fatigue, anemia, kidney problems (myeloma)
↓ What Low IgG (Immunoglobulin G) Means
Immunodeficiency—increased risk of infections. Could be primary (genetic: CVID, X-linked agammaglobulinemia) or secondary (medications like rituximab, protein loss, or hematologic malignancy).
Common symptoms:
Recurrent sinusitis, bronchitis, pneumonia · Recurrent ear infections · Chronic diarrhea (GI infections) · Unexplained bronchiectasis
Why It Matters
When normal:
Backbone of humoral immunity
Protects against bacteria and viruses
Low IgG explains recurrent infections
Monoclonal IgG spike screens for myeloma/MGUS
Risks if abnormal:
Low: recurrent sinopulmonary infections, pneumonia, sepsis
Very low (<400 mg/dL): may need IgG replacement therapy
Monoclonal elevation: myeloma, MGUS, lymphoproliferative disease
What Can Cause Abnormal Levels?
Primary Immunodeficiency (low)
25% likelyCommon variable immunodeficiency (CVID) is the most common symptomatic primary immunodeficiency in adults.
Chronic Infection/Inflammation (high)
40% likelyPolyclonal IgG elevation is a normal response to chronic antigenic stimulation.
Rituximab/B-cell Depleting Therapy (low)
Rituximab depletes B cells, leading to secondary hypogammaglobulinemia.
Nephrotic Syndrome (low)
IgG is lost in urine with heavy proteinuria.
Multiple Myeloma (monoclonal high)
Malignant plasma cells produce one type of IgG in excess while suppressing normal Ig.
Chronic Liver Disease (polyclonal high)
Cirrhosis causes polyclonal hypergammaglobulinemia from decreased hepatic clearance and increased gut-derived antigens.
What You Can Do
If low IgG with recurrent infections: quantitative immunoglobulin panel
Impact: Measures IgG, IgA, IgM to characterize deficiency \u00B7 Timeline: One-time
Pneumococcal vaccine response testing if IgG borderline low
Impact: Functional antibody test—can you make specific antibodies? \u00B7 Timeline: One-time
If lifestyle changes aren't enough:
If monoclonal spike: SPEP, serum free light chains, bone marrow biopsy consideration
Impact: Workup for myeloma vs MGUS \u00B7 Timeline: Urgent
Recommended retest: q6-12 months if on replacement therapy; SPEP annually if MGUS
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