Increased synthesis of immunoglobulins in the CNS indicates an immune stimulus and can be seen in infectious, inflammatory and autoimmune disorders affecting the CNS.
CNS IgG synthesis rate in mg/day =
= 5 * (((CSF IgG in mg/dL) - ((serum IgG in mg/dL) / A)) - (((CSF albumin in mg/dL) - ((serum albumin in mg/dL) / B)) * 0.43 * (serum IgG in mg/dL) / (serum albumin in mg/dL)))
where:
• A = method dependent variable indicating average CSF-to-serum ratio for IgG; this varies from 341 (Wallach) to 369 (Jacobs, Tourtellotte)
• B = method dependent variable indicating the average serum-to-CSF ratio for albumin; this varies from 169 (Wallach) to 230 (Jacobs, Tourtellotte)
• 0.43 is the ratio of the molecular weight of albumin to that of IgG
• All proteins in mg/dL (Henry, 1996)
Interpretation:
• normal: <= 3 mg/day
• increased: > 3 mg/day
Limitation:
• Blood contamination can markedly affect results, causing false positives.
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