Immunoglobulin G (IgG) by CSF

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Measures immunoglobulin in CSF.

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Immunoglobulin G (IgG) by CSF - Comprehensive Medical Test Guide

Why is it done?
- Measures immunoglobulin G antibodies present in cerebrospinal fluid to assess immune response in the central nervous system
- Diagnoses central nervous system (CNS) infections including meningitis, encephalitis, and neurosyphilis
- Evaluates autoimmune and demyelinating diseases such as multiple sclerosis, neuromyelitis optica, and autoimmune encephalitis
- Detects viral infections of the CNS including herpes simplex virus, varicella-zoster virus, measles, and tuberculosis
- Assesses intrathecal immunoglobulin synthesis and blood-brain barrier integrity
- Typically performed when patients present with symptoms of meningitis, encephalitis, unexplained neurological symptoms, or suspected demyelinating disease
Normal Range
- Normal CSF IgG concentration: 0.5-6.1 mg/L (or 0.0005-0.0061 g/L)
- IgG Index (most commonly used): Less than 0.66 is considered normal
- Formula: IgG Index = (CSF IgG/CSF albumin) ÷ (Serum IgG/Serum albumin)
- IgG Synthesis Rate: Normal is less than 3.3 mg/day
- Oligoclonal Bands (OCB): Negative (absent in serum but present in CSF suggests intrathecal synthesis)
- Interpretation: Normal results indicate no significant intrathecal IgG synthesis and absence of CNS inflammation or infection
- Elevated IgG levels suggest active CNS infection, inflammation, or immune-mediated disease requiring further clinical correlation
Interpretation
- Elevated IgG Index (>0.66) or Increased IgG Synthesis:
  - Indicates intrathecal immunoglobulin synthesis occurring within the CNS
  - Suggests CNS infection (bacterial, viral, tuberculous meningitis) or inflammatory disease
  - Highly associated with multiple sclerosis when paired with oligoclonal bands
- Oligoclonal Bands Present in CSF only:
  - Highly suggestive of multiple sclerosis (present in 90-95% of MS patients)
  - Also seen in CNS infections, inflammatory, and demyelinating conditions
- Normal IgG with Other Findings:
  - May still indicate early stage infection before immune response develops
  - Requires correlation with clinical presentation, CSF cell count, glucose, protein, and culture results
- Factors Affecting Results:
  - Timing of collection relative to symptom onset affects detection
  - Blood contamination during lumbar puncture can elevate results
  - Compromised blood-brain barrier allows serum IgG to cross into CSF
  - IgG Index calculation accounts for serum IgG levels and albumin ratios
Associated Organs
- Primary Organ Systems:
  - Central nervous system (brain and spinal cord)
  - Immune system (antibody-producing plasma cells and B lymphocytes)
  - Meninges (protective membranes surrounding brain and spinal cord)
- Conditions Associated with Abnormal Results:
  - Infections: Bacterial meningitis, viral meningitis, tuberculous meningitis, fungal meningitis, neurosyphilis, Lyme disease
  - Demyelinating diseases: Multiple sclerosis, neuromyelitis optica, Devic disease
  - Inflammatory conditions: Encephalitis, acute disseminated encephalomyelitis (ADEM), neuroimmunologic disorders
  - Autoimmune encephalitis: Anti-NMDA receptor encephalitis, anti-GABAb receptor encephalitis, limbic encephalitis
  - Chronic conditions: Subacute sclerosing panencephalitis (SSPE), progressive multifocal leukoencephalopathy (PML)
- Potential Complications of Abnormal Results:
  - Untreated CNS infection can lead to neurological damage, permanent disability, or death
  - Demyelinating diseases may progress to severe neurological impairment if untreated
  - Autoimmune conditions require prompt identification and treatment to prevent seizures or cognitive decline
Follow-up Tests
- Additional CSF Analysis Tests:
  - CSF IgM and IgA to assess different antibody responses
  - Oligoclonal bands (OCB) testing for demyelinating disease differentiation
  - CSF cell count and differential to evaluate inflammation
  - CSF glucose and protein levels
  - CSF bacterial culture and sensitivity
  - CSF Gram stain and other stains
  - CSF viral PCR panels (HSV, VZV, enterovirus, etc.)
- Serum Testing:
  - Serum IgG level and albumin (necessary for IgG Index calculation)
  - Serum oligoclonal bands for comparison
  - Blood cultures if infection suspected
  - Serum viral serology (HSV, VZV, measles, etc.)
- Imaging Studies:
  - Brain MRI with and without contrast (for demyelinating lesions, inflammation)
  - Spinal cord MRI if myelitis or spinal involvement suspected
  - Brain CT scan for acute settings or when MRI contraindicated
- Specialized Testing:
  - Autoimmune encephalitis panel (NMDA-R, GABAb-R, LGI1, CASPR2 antibodies)
  - Paraneoplastic antibody panels if malignancy suspected
  - Lyme disease serology (ELISA and Western blot)
  - Syphilis serology (RPR, FTA-ABS, TP-PA)
- Monitoring Frequency:
  - Multiple sclerosis: Repeat CSF IgG and OCB annually or with clinical changes
  - CNS infections: Follow-up lumbar puncture may be performed 48-72 hours after treatment initiation
  - Autoimmune encephalitis: Serial CSF examination during treatment course
Fasting Required?
- Fasting: No
- This test does not require fasting as it is performed on cerebrospinal fluid obtained via lumbar puncture, not blood
- Patient Preparation Requirements:
  - Informed consent must be obtained before lumbar puncture procedure
  - Patient should be positioned in lateral recumbent (side-lying) position or sitting upright and flexed forward
  - Empty bladder before procedure
  - Baseline neurological examination may be performed
- Medications:
  - Anticoagulants: Warfarin, DOACs should be reviewed; discuss with physician regarding continuation
  - Platelet aggregation inhibitors: Aspirin, clopidogrel typically do not require discontinuation but inform provider
  - Other medications: Continue as prescribed unless instructed otherwise by physician
- Post-Procedure Instructions:
  - Remain lying flat for 30-60 minutes to prevent post-dural puncture headache
  - Increase fluid intake to promote CSF production
  - Monitor for complications such as severe headache, neurological changes, or local pain

How our test process works!