Preanalytical stability of plasma biomarkers for Alzheimer's disease pathology

Introduction

Plasma tests have demonstrated high diagnostic accuracy for identifying Alzheimer's disease pathology. To facilitate the transition to clinical utility, we assessed whether plasma storage duration and temperature affect the biomarker concentrations.

Methods

Plasma samples from 13 participants were stored at +4°C and +18°C. Concentrations of six biomarkers were measured after 2, 4, 6, 8, 10, and 24 h by single molecule array assays.

Results

Phosphorylated tau 181 (p-tau181), phosphorylated tau 231 (p-tau231), neurofilament light (NfL), and glial fibrillary acidic protein (GFAP) concentrations were unchanged both when stored at +4°C and +18°C. Amyloid-β 40 (Aβ40) and amyloid-β 42 (Aβ42) concentrations were stable for 24 h at +4°C but declined when stored at +18°C for longer than 6 h. This decline did not affect the Aβ42/Aβ40 ratio.

Discussion

Plasma samples can be stored for 24 h at +4°C or +18°C and result in valid assay results for p-tau181, p-tau231, Aβ42/Aβ40 ratio, GFAP, and NfL.

HIGHLIGHTS

Plasma samples were stored for 24 h at +4°C and +18°C, mimicking clinical practice.Concentrations for Alzheimer's disease biomarkers were measured at six time-points.p-tau181, p-tau231, NfL, and GFAP concentrations were unchanged during the experiment.Storage at +18°C affected Aβ40 and Aβ42 concentrations while storage at +4°C did not. The Aβ42/Aβ40 ratio was unaffected.These plasma tests seem suitable for use in general practice.

Body mass index trajectories and associations with cognitive decline in people with Lewy body dementia and Alzheimer's disease

Background and Aims

In older adults with dementia, low body mass index (BMI) is associated with higher mortality and other adverse health outcomes. BMI or nutritional status trajectories from diagnosis have not yet been well described in dementia, especially in people with Lewy body dementia (LBD); a group that has a poorer prognosis. With this study, we aimed to evaluate the BMI trajectory in people diagnosed with mild LBD and Alzheimer's disease (AD).

Methods

The Dementia Study of Western Norway is a cohort study with annual assessments. Five-year measurements of BMI from 196 patients (LBD = 85 and AD = 111) diagnosed with mild dementia were analyzed using adjusted linear mixed-effects models.

Results

There were no differences between LBD and AD in baseline BMI, age, or mini-mental status examination (MMSE). During the follow-up, we observed a significant decrease in BMI in the LBD group across the study period (estimation [Est.]: -0.63, SE: 0.14; p < 0.001). By contrast, there was no significant change in BMI trajectory associated with AD diagnosis (Est.: 0.05, SE: 0.15; p = 0.730). Further, the introduction of an interaction term between diagnosis and time in the study showed that this difference (BMI trajectories) was significant (Est.: -0.63, SE: 0.14; p < 0.001). In addition, there was a significant interaction between MMSE total score and the follow-up time; the lower the MMSE, the lower the BMI (Est.: 0.01, SE: 0.01; p = 0.044).

Conclusion

In LBD, BMI significantly decreased with disease progression. In addition, low cognitive performance was associated with a reduction in BMI. These results highlight the importance of BMI evaluation in people with dementia, particularly patients diagnosed with LBD, and suggest that patients with LBD could be targeted for dietary intervention to maintain body weight.