Cerebrospinal fluid/serum albumin quotient (Q-Alb) is not increased in Alzheimer’s disease compared to neurological disease controls: a retrospective study on 276 patients

Background: The cerebrospinal fluid (CSF)/serum albumin quotient (Q-Alb) is a marker of the blood-CSF barrier (BCSFB) and possibly of the blood–brain barrier (BBB). The latter is known to be altered in Alzheimer’s disease (AD) based on neuropathological and neuroimaging studies. Following investigations performed on clinically diagnosed cohorts, we aimed at comparing Q-Alb in cognitively impaired patients with neurochemical demonstration of AD pathophysiology and neurological disease controls (NDCs). Methods: We evaluated N = 144 AD patients (MCI, N = 43; AD dementia — ADD, N = 101) and N = 132 NDCs. AD patients were all A + according to the A/T/N framework and were neurochemically classified based on T and N parameters. Results: Q-Alb did not significantly differ between AD patients and NDCs. Moreover, it was not associated with disease stage (MCI vs. ADD), MMSE score, or CSF AD biomarkers. Discussion: Our study indicates that BCSFB dysfunction is not a specific feature of AD. When interpreting Q-Alb as a marker of the BBB, the lack of difference from NDCs might be due to BBB dysfunction widely occurring in other neurological, non-degenerative, conditions or — more probably — to low sensitivity of this biochemical parameter towards subtle BBB alterations causing leakage of molecules smaller than albumin. Furthermore, Q-Alb is not associated with the degree of global cognitive deterioration in AD, nor with CSF AD neurochemical biomarkers.