Fig. 1
From: Barrier dysfunction or drainage reduction: differentiating causes of CSF protein increase
Variation of the immunoglobulin G quotient with that of albumin as depicted in Reiber diagrams. a Displays the empirically established relationship between the concentration of IgG in CSF relative to its concentration in blood serum (IgG quotient, QIgG) and the correspondingly defined albumin quotient (QAl). b Depicts the normal range of albumin quotients, corresponding to the area in a marked with the black square. Reiber demonstrated that the average quotient variation (black line) and upper and lower bounds (green dashed lines) follow the hyperbolic function \(Q_{IgG} = \frac{a}{b}\sqrt {Q_{Al}^{2} + b^{2} } - c\) [32]. He also showed that the population variation coefficient (CV), defined for a given albumin quotient as \(CV = \frac{{\Delta Q_{IgG} }}{{0.5\cdot\left( {Q_{{IgG_{upper limit} }} + Q_{{IgG_{lower limit} }} } \right)}}\), remains constant over the entire range of investigated albumin quotients. QIgG values above the upper bound are indicative of a blood-CNS barrier dysfunction