Protein analyses in cerebrospinal fluid. I. Influence of concentration gradients for proteins on cerebrospinal fluid/serum albumin ratio.

Concentration gradients in lumbar cerebrospinal fluid (CSF) for albumin and IgG were studied in 8 healthy individuals and 44 neuropsychiatric patients by serial sampling of 6 successive portions of CSF, each containing 4 ml, in all 24 ml. Significant and identical decreases between the first (0-4th ml) and the last (21st-24th ml) portions were found for CSF-albumin (21% decrease, p < 0.0001) and CSF-IgG (21% decrease, p < 0.0001). Therefore, the CSF/serum albumin ratio also showed a significant gradient with a 21% decrease (p < 0.0001), while no gradients were found to the IgG index. These results imply that analyses of proteins in the CSF should be performed on a standardized volume of CSF, preferably the first 12 ml, to allow comparisons of scientific results between various patient groups and controls and between different laboratories and to increase the validity of protein analyses in clinical practice.