CASF - Clinical: IgG/Albumin Ratio, Spinal Fluid

Test Catalog

Test Name

Test ID: CASF    
IgG/Albumin Ratio, Spinal Fluid

Useful For Suggests clinical disorders or settings where the test may be helpful

The cerebrospinal fluid (CSF) index is useful in the diagnosis of individuals with multiple sclerosis. In the absence of a paired CSF and serum specimen, the CSF IgG/albumin ratio can be assessed.


The index is independent of the activity of the demyelinating process.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Elevation of IgG levels in the cerebrospinal fluid (CSF) of patients with inflammatory diseases of the central nervous system (CNS) (multiple sclerosis, neurosyphilis, acute inflammatory polyradiculoneuropathy, subacute sclerosing panencephalitis) is due to local (CNS) synthesis of IgG.


The two most commonly used diagnostic laboratory tests for multiple sclerosis are CSF index and oligoclonal banding. The CSF index is the CSF IgG to CSF albumin ratio compared to the serum IgG to serum albumin ratio. 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 central nervous system.  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.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

CSF IgG: 0.0-8.1 mg/dL

CSF albumin: 0.0-27.0 mg/dL

CSF IgG/albumin: 0.00-0.21

Interpretation Provides information to assist in interpretation of the test results

Cerebrospinal fluid IgG index is positive (elevated) in approximately 80% of patients with multiple sclerosis.


Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

The cerebrospinal fluid (CSF) index can be elevated in other inflammatory demyelinating diseases such as neurosyphillis, acute inflammatory polyradiculoneuropathy, and subacute sclerosing panencephalitis. Oligoclonal banding in 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 over 90%.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Tourtellotte WW, Walsh MJ, Baumhefner RW, Staugaitis SM, Shapshak P: The current status of multiple sclerosis intra-blood-brain-barrier IgG synthesis. Ann NY Acad Sci 436:52-67,1984

2. Bloomer LC, Bray PF: Relative value of three laboratory methods in the diagnosis of multiple sclerosis. Clin Chem 27(12):2011-2013,1981

3. Hische EAH, vander Helm HJ: Rate of synthesis of IgG within the blood-brain barrier and the IgG index compared in the diagnosis of multiple sclerosis. Clin Chem 33(1):113-114,1987

4. Swanson JW: Multiple Sclerosis: Update in diagnosis and review of prognastic factors. Mayo Clin Proc 64:577-585,1989

5. Markowitz H, Kokmen E: Neurologic diseases and the cerebrospinal fluid immunoglobulin profile. Mayo Clin Proc 58:273-274,1983