What this test measures
Immunoglobulin G (IgG) is the most abundant antibody class in blood, making up about 75% of total serum immunoglobulin. It is produced after maturation of the immune response (class-switched from IgM), provides long-term immunity after infection or vaccination, and crosses the placenta to protect newborns.
The test measures total serum IgG (all four subclasses — IgG1, IgG2, IgG3, IgG4 combined), reported in mg/dL or g/L. Subclass measurement is a separate test, used when total IgG is normal but selective subclass deficiency is suspected.
Why it matters
Low IgG (hypogammaglobulinaemia) is a major cause of recurrent bacterial infections — sinopulmonary infections, otitis, pneumonia, severe gastroenteritis. Common causes include common variable immunodeficiency (CVID), X-linked agammaglobulinaemia, drug-induced (rituximab, anticonvulsants), nephrotic syndrome, protein-losing enteropathy, and severe burns. Diagnosis often leads to IV immunoglobulin replacement therapy, which is life-changing.
High IgG points to chronic inflammatory or autoimmune disease (SLE, RA, chronic infection), monoclonal gammopathy (IgG myeloma or MGUS — confirmed with SPEP and free light chains), or IgG4-related disease (a fibroinflammatory condition recognised increasingly in Indian clinics). Polyclonal high IgG is non-specific; monoclonal high IgG with an M-protein band requires haematology workup.
How to prepare
No fasting required. Continue all medications. Disclose any history of recurrent infections, immunodeficiency, recent IV immunoglobulin therapy (which artificially raises serum IgG for weeks), any biological therapy, or known plasma cell disorder.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Immunoglobulin G (mg/dL)[1][2][3] | Adult 700 – 1600 mg/dL (lab-specific) | < 700 mg/dL: hypogammaglobulinaemia — CVID, X-linked agammaglobulinaemia, hyper-IgM syndrome, transient hypogammaglobulinaemia of infancy, drug-induced (rituximab, anti-epileptic drugs, steroids), nephrotic syndrome, protein-losing enteropathy, severe burns, multiple myeloma with immune paresis. | > 1600 mg/dL: polyclonal — chronic infection (TB, HIV, chronic viral hepatitis), chronic autoimmune disease (SLE, RA, autoimmune hepatitis), chronic liver disease, IgG4-related disease. Monoclonal (with M-spike) — IgG myeloma, MGUS, Waldenström. |
IgG patterns and what they suggest
| Pattern | Likely cause |
|---|---|
| Low IgG + low IgA + low IgM | CVID, agammaglobulinaemia, severe protein loss |
| Low IgG + normal IgA + normal IgM | IgG subclass deficiency, drug-induced |
| High IgG (polyclonal, no M-spike) | Chronic infection or autoimmune disease |
| High IgG (monoclonal, M-spike on SPEP) | IgG myeloma, MGUS, Waldenström |
| Very high IgG (IgG4 elevated) | IgG4-related disease |
Frequently asked questions
What does low IgG mean?
Low total IgG (hypogammaglobulinaemia) causes increased susceptibility to bacterial infections, especially sinopulmonary. Common causes include CVID (most frequent in adults), drug-induced (rituximab, anti-epileptics, steroids), nephrotic syndrome, severe protein loss, and rare X-linked agammaglobulinaemia. Workup includes IgG subclasses, vaccine response testing, and sometimes lymphocyte phenotyping.
Is high IgG always bad?
No. Polyclonal high IgG often reflects chronic inflammation or infection (common in India — TB, chronic HIV, chronic hepatitis). The real concern is monoclonal high IgG — IgG with an M-protein band on serum protein electrophoresis — which suggests IgG myeloma or MGUS and needs haematology workup.
What is IgG4-related disease?
An increasingly recognised fibroinflammatory disease where IgG4-producing plasma cells infiltrate multiple organs — pancreas (autoimmune pancreatitis), salivary glands, kidneys, retroperitoneum. Elevated serum IgG4 (> 135 mg/dL) supports the diagnosis but is not specific; tissue biopsy is the gold standard.
Should I test IgG subclasses?
When total IgG is normal but recurrent infections persist, IgG subclass deficiency (most often IgG2 in adults) may be the cause. Subclass measurement is a separate test ordered by an immunologist.
Does IV immunoglobulin affect the test?
Yes — IV immunoglobulin therapy raises serum IgG for weeks. If you have recently received IVIG, baseline IgG cannot be assessed until at least 3–4 months after the last dose.
Are children's reference ranges different?
Yes. Maternal IgG protects babies for the first 6 months, then falls; the baby's own IgG production rises through childhood. Use age-specific reference ranges. "Transient hypogammaglobulinaemia of infancy" is a common, usually self-limiting cause of low IgG in toddlers.
What is the treatment for low IgG?
Identify the cause (primary immunodeficiency vs secondary). For primary humoral immunodeficiency with recurrent infections, regular IV or subcutaneous immunoglobulin replacement (IVIG / SCIG) is the standard of care, available in India through tertiary immunology centres.
Related Immunology tests
Tests commonly ordered alongside IMMUNOGLOBULIN G (IGG), or that help interpret an unexpected result.
Sources & references
- NIH MedlinePlus — Immunoglobulin Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Immunoglobulin G · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — Immunoglobulin G · accessed 2026-05-30T00:00:00.000Z
- AAAAI — Primary Immunodeficiency · accessed 2026-05-30T00:00:00.000Z
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