CSF Immunoglobulin G (IgG) Index Test

This test measures the level of IgG antibodies in your cerebrospinal fluid to help check for diseases of the central nervous system, such as multiple sclerosis.

What this test measures

CSF stands for cerebrospinal fluid. IgG stands for immunoglobulin G, a type of antibody. The CSF IgG index measures the levels of IgG in your cerebrospinal fluid.

What your results mean

Reference ranges vary by laboratory and by your age and sex. MedlinePlus does not publish a single normal range for this test — always read your result against the range printed on your own lab report and discuss it with your provider.

Higher-than-normal results

A CSF IgG index that's higher than normal may be a sign of an infection or an inflammatory or autoimmune condition that affects your central nervous system, such as multiple sclerosis, transverse myelitis, neurosyphilis, connective tissue disorders, Guillain-Barre syndrome, or encephalitis caused by herpes simplex.

Lower-than-normal results

A CSF IgG index that's lower than normal may be a sign that your body is unable to make enough IgG antibodies, and you are likely to get sick with infections.

Frequently asked questions

What does CSF stand for?

CSF stands for cerebrospinal fluid.

What is IgG?

IgG stands for immunoglobulin G, a type of antibody that your immune system makes to fight germs.

Why is a CSF IgG index done?

It is used to check for diseases of the central nervous system, often to help diagnose multiple sclerosis.

Can a CSF IgG index alone diagnose multiple sclerosis?

No, a CSF IgG test alone can't diagnose MS. You may need more tests.

What does a low CSF IgG index mean?

A low index may mean your body cannot make enough IgG antibodies, making you more likely to get infections.

Sources

MedlinePlus: CSF Immunoglobulin G (IgG) Index — NIH MedlinePlus

Last updated July 7, 2026. Information is aggregated from official public sources and is not a substitute for professional medical care.