The two most commonly used diagnostic laboratory tests for multiple sclerosis are the CSF index and oligoclonal banding. The CSF index is the IgG-to-albumin ratio in CSF compared to the IgG-to-albumin ratio in serum. The CSF index is, therefore, an indicator of the relative amount of CSF IgG compared to serum, and any increase in the index is a reflection of IgG production in the CNS. The IgG synthesis rate is a mathematical manipulation of the CSF index data and can also be used as a marker for CNS inflammatory diseases. The index is independent of the activity of the demyelinating process.
Normal range:
IgG, CSF: 0.0 " “6.0 mg/dL
Albumin, CSF: 0 " “35 mg/dL
IgG-to-albumin ratio, CSF: 0.09 " “0.25
Use
Diagnosis of individuals with multiple sclerosis
Interpretation
Increased In
Multiple sclerosis.
High normal values may indicate degenerative diseases such as cerebral or cerebellar atrophy, amyotrophic sclerosis, or brain tumor.
Limitations
The CSF index can be elevated in other inflammatory demyelinating diseases such as neurosyphilis, acute inflammatory polyradiculoneuropathy, and subacute sclerosing panencephalitis.
Oligoclonal banding in the CSF is slightly more sensitive (85%) than the CSF index. The use of CSF index plus oligoclonal banding has been reported to increase the sensitivity to >90%.
Normal levels can occur in incomplete obstruction of the spinal canal.
Increase in albumin alone can be a result of a lesion in the choroid plexus or a blockage in the flow of CSF.
Determination of myelin basic protein in CSF may be of use in diagnosis of multiple sclerosis or other active demyelinating processes.