CSF IgG Index

An elevated CSF IgG Index typically indicates that the immune system is producing IgG antibodies within the central nervous system (CNS)—a phenomenon known as intrathecal IgG synthesis. This finding is not normal and usually suggests inflammation or immune activation inside the brain or spinal cord.

What an Elevated CSF IgG Index May Indicate:

1. Multiple Sclerosis (MS)

   • One of the most common causes of an elevated CSF IgG index.

   • Seen alongside oligoclonal bands and clinical symptoms such as optic neuritis, numbness, or motor weakness.

2. Other Demyelinating Disorders

   • Neuromyelitis optica (NMO), transverse myelitis, or other autoimmune neurological diseases.

3. Chronic Central Nervous System Infections

   • Conditions like neurosyphilis, HIV-associated neurocognitive disorders, Lyme disease, or tuberculous meningitis can cause elevated intrathecal IgG.

4. Autoimmune or Inflammatory Conditions

   • Such as lupus cerebritis, sarcoidosis, or other systemic diseases with CNS involvement.

Important Notes:

• A CSF IgG Index ≥ 0.7–0.85 (depending on the lab's reference range) is considered elevated.

• It should always be interpreted alongside other tests, especially:

  • Oligoclonal banding (OCBs)

  • MRI of the brain and spine

  • Clinical symptoms and neurological exam findings

Takeaway:

An elevated index suggests abnormal immune activity in the CNS and may support the diagnosis of multiple sclerosis or another inflammatory or infectious neurological condition. Further testing and clinical correlation are essential to determine the exact cause.

The CSF IgG Index is a valuable marker for detecting immune activity within the brain or spinal cord, often helping diagnose or monitor diseases like multiple sclerosis. Results should always be interpreted alongside other tests (e.g., oligoclonal bands, MRI) and clinical findings by a healthcare provider.