The intactness of the blood-brain barrier can be assessed by comparing levels of albumin in serum and CSF.
CSF-to-serum albumin index =
= (CSF albumin in mg/dL) / (serum albumin in g/dL)
Interpretation:
• The normal range is 4-8; if the CSF albumin is expressed in g/dL, the normal value is 0.004-0.008
• values of 9-14 indicate slight impairment in the blood-brain barrier
• values of 15-30 indicate moderate impairment
• values over 30 indicate severe impairment
• values reach adult levels at about 6 months; younger infants have slightly elevated values reflecting immaturity of the barrier
• values tend to increase slowly after age 40
Limitations:
• A traumatic CSF tap results in a false elevation of the index.
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Specialty: Immunology/Rheumatology