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.