CSF IgG Index

This index provides good separation between protein increase from increased permeability of the blood brain barrier and increased CNS IgG production.

CSF IgG index =

= ((CSF IgG in mg/dL) * (serum albumin in g/dL)) / ((CSF albumin in mg/dL) * (serum IgG in g/dL))

which is equivalent to:

CSF IgG index =

= (CSF-to-serum IgG index) / (CSF-to-serum albumin index)

Interpretation

Normal CSF IgG <= 8.4 mg/dL

Normal CSF albumin <= 26.0 mg/dL

Normal index: < =0.77 mg/dL

An elevated index ( > 0.77 mg/dL) is seen in:

(1) 58% definite multiple sclerosis

(2) 42% probable multiple sclerosis

(3) 33% inflammatory neurologic diseases

(4) 12% noninflammatory neurologic diseases.

For multiple sclerosis, it has a sensitivity of 88% and specificity of 95%.

Limitation:

• Blood contamination can markedly affect results, causing false positives.

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