IgG/Albumin Ratio, CSF (IGARCF)

This test may be helpful in the evaluation of intrathecal synthesis of IgG in individuals with clinical suspicion of inflammatory diseases of the central nervous system (CNS), especially multiple sclerosis [1]. Intrathecal synthesis of IgG can be more specifically demonstrated by paring IgG/albumin ratios in the cerebrospinal fluid (CSF) and serum to calculate IgG index [2].

Elevated IgG levels in the CSF may be caused by increased intrathecal synthesis of IgG, increased permeability of blood-brain barrier, or both. Because albumin is not synthesized or metabolized in the CSF, it can be used to evaluate the permeability of the blood-CSF barrier. To demonstrate intrathecal synthesis of IgG specifically, IgG and albumin levels in the CSF and serum can be used to calculate IgG index [1].

In patients with multiple sclerosis, intrathecal synthesis of IgG may be evaluated with several assays. IgG/albumin ratio in the CSF may be elevated in about 70% of the patients. IgG index, calculated with paired IgG/albumin ratios in the CSF and serum, may be elevated in about 80% of patients. Oligoclonal bands may be detected in up to 95% of the patients [1-3].

Intrathecal synthesis of IgG may also be caused by other CNS inflammatory diseases, such as chronic meningoencephalitis, subacute sclerosing panencephalitis, and Guillain-Barre syndrome [1].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. Johnson AM, et al. Amino acids, peptides, and proteins. In: Burtis CA, et al. eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 4th ed. Elsevier Inc; 2006:578-580.
2. Hershey LA, et al. Ann Neurol. 1980;8(4):426-434.
3. Giesser BS. Neurol Clin. 2011;29(2):381-388.