CSF IgG Index
Info
CSF IgG
unit mg/dL mg/L
CSF Albumin
unit mg/dL mg/L
Serum IgG
unit mg/dL mg/L
Serum Albumin
unit g/dL g/L
R e s u l t s
The CSF IgG Index
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CSF IgG Index

The IgG Index is superior to the IgG to albumin ratior measurement of IgG in CSF alone. It may be used to:

  • To evaluate the integrity and permeability of the blood-CSF barrier
  • To measure the local synthesis of IgG within the CNS
  • Evaluation of several conditions (see below); but most notably:
    • IgG index is the first CSF abnormality in early MS with >0.7 in 86-94% cases
    • Elevated IgG and IgG index may be detected in neurosarcoidosis
  • A traumatic tap invalidates results

Immunoglobulin G (IgG): Albumin Index (CSF) may be elevated in:

  • Multiple sclerosis (Elevated index in 85% of MS patients)
  • Subacute sclerosing leukoencephalitis
  • Subacute sclerosing panencephalitis
  • Neurosyphilis
  • Tumors of the brain and meninges
  • Chronic CNS infections
  • Neurosarcoidosis

General Notes on IgG Index

  • A traumatic tap invalidates results
  • Normal total range of CSF IgG is <4 mg/dL (<40 mg/L)
  • Normal IgG index is <0.7
  • CSF immunoglobulins can arise primarily from three causes:
    • Secondary tan increase in plasma immunoglobulin as in multiple myeloma
    • Damage to, or impairment of the blood-brain barrier
    • Local synthesis in the CNS as in multiple sclerosis and other chronic inflammatory disorders of the CNS
  • The IgG index method is superior tthe IgG-to-albumin ratior measurement of IgG only. It is calculated with the following formula:
    • CSF IgG Index = (CSF IgG × serum albumin × 1000)/(CSF albumin × serum IgG)

For Conventional Units:

  • CSF IgG = mg/dL
  • CSF Albumin = mg/dL
  • Serum IgG = mg/dL
  • Serum Albumin = grams/dL

Reference:

  • Hische EA, Van der helm HJ, Van walbeek HK. The cerebrospinal fluid immunoglobulin G index as a diagnostic aid in multiple sclerosis: a Bayesian approach. Clin Chem. 1982;28(2):354-5.
  • Link H, Tibbling G. Principles of albumin and IgG analyses in neurological disorders. III. Evaluation of IgG synthesis within the central nervous system in multiple sclerosis. Scand J Clin Lab Invest. 1977;37(5):397-401.