IgG4 (immunoglobulin G4)
One of the four subclasses of the IgG antibody. Its main clinical use is in IgG4-related disease — an unusual condition in which IgG4-rich inflammation and scarring affect organs such as the pancreas, bile ducts, salivary glands and others — where a markedly raised level supports the diagnosis.
What it measures
IgG, the main antibody in the blood, comes in four subclasses (IgG1 to IgG4); IgG4 is normally the smallest fraction. Measuring it specifically is useful in one distinctive setting: IgG4-related disease. This is a fibro-inflammatory condition, recognised relatively recently, in which tissue becomes infiltrated by IgG4-producing immune cells and develops a characteristic pattern of inflammation and scarring (fibrosis), often forming tumour-like swellings. It can affect almost any organ, but classically involves the pancreas (autoimmune pancreatitis), the bile ducts (IgG4-related sclerosing cholangitis, which can mimic other bile-duct diseases and cancers), the salivary and tear glands, the kidneys, the aorta and the retroperitoneum. A markedly raised serum IgG4 supports the diagnosis and can help distinguish these conditions from look-alikes such as pancreatic cancer or primary sclerosing cholangitis. However, the level is not perfect — it can be normal in genuine disease and mildly raised in other conditions — so diagnosis rests on the combination of the clinical picture, imaging, the IgG4 level and, crucially, a biopsy showing the typical tissue changes. IgG4 is also followed to help monitor disease activity and response to treatment.
What a high value can mean
- IgG4-related disease — the key use; a markedly raised level supports this fibro-inflammatory condition affecting the pancreas, bile ducts and other organs.
- Autoimmune pancreatitis (type 1) — a common form of IgG4-related disease.
- IgG4-related sclerosing cholangitis — bile-duct involvement that can mimic other diseases and cancers.
- Mildly raised in some other conditions — certain allergic, parasitic and inflammatory states, so a modest rise is not specific.
What a low value can mean
- Normal or low — the expected result, and does not exclude IgG4-related disease (the level can be normal in genuine cases).
- A falling level on treatment — can indicate a response, and it is used to help monitor disease activity.
When to discuss with a doctor
IgG4 is a specialist test, used mainly when IgG4-related disease is suspected — for example unexplained pancreatic or bile-duct inflammation, tumour-like organ swellings, or enlarged salivary or tear glands — rather than as a general test. A markedly raised level supports the diagnosis and can help distinguish these conditions from mimics such as pancreatic cancer, but the level alone is neither necessary nor sufficient: a normal IgG4 does not exclude the disease, and a mild rise can occur in other conditions. The diagnosis is made by a specialist from the whole picture, usually confirmed on a biopsy, and IgG4 is then followed to help monitor treatment. Mediora.AI shows IgG4 alongside total IgG, the other immunoglobulins and the liver enzymes so it is read in context; the diagnosis and treatment belong with your specialist team.