Biomarkers

Plasma biomarkers of Alzheimer's disease (AD) pathology are frequently tested in research settings, limiting generalizability of findings. Using electronic health records, we evaluated plasma biomarkers - phosphorylated tau 217 (p-tau217), β-amyloid 1-42/1-40 (Aβ42/Aβ40) and p-tau217/Aβ42 - in a real-world, racially diverse data set with multimorbidities.

Participants (n = 683; 298 Black/African American, 385 White) were selected from the University of Pennsylvania Medicine Biobank. International Classification of Disease (ICD) codes determined AD dementia (ADD; n = 79), mild-cognitive impairment (MCI; n = 239), unspecified/non-AD cognitive impairment (CI; n = 143) and cognitively normal cases (n = 222). ICD codes determined histories of diabetes, depression, traumatic brain injury, hypertension, alcoholism, and hearing/visual loss, and body mass index (BMI). Blood was analyzed for APOE ε4, ALT, creatinine, eGFR, albumin, and LDL-cholesterol. Plasma analytes were assayed using Fujirebio Lumipulse; previously established cutpoints determined AD status: "AD+", "AD-", or "Undetermined". Multivariable models tested how morbidities, age, sex, and race related to plasma levels.

Plasma p-tau217/Aβ42 (Figure 1) was increased in MCI (β=0.46, p <0.001) and ADD compared to Normal cognition (β=0.93, p <0.001); p-tau217/Aβ42 increased with age (β=0.30, p <0.001), female sex (β=0.25, p = 0.029), APOE ε4 (β=0.31, p = 0.001), and creatinine (β=0.25, p = 0.024), with no difference by race (p = 0.15) Plasma p-tau217 (Figure 2) was increased in MCI (β=0.38, p = 0.001), ADD (β=0.83, p <0.001), with age (β=0.23, p <0.001), female sex (β=0.24, p = 0.015), APOE ε4 (β=0.24, p = 0.006), higher creatinine (β=0.37, p <0.001), lower eGFR (β=-0.20, p = 0.041), and lower albumin (β=-0.13, p = 0.003); difference by race was not significant (β=-0.18, p = 0.053). Plasma Aβ42/Aβ40 (Figure 3) decreased with age (β=-0.18, p = 0.013), higher ALT (β=-0.13, p = 0.045), higher LDL-cholesterol (β=-0.17, p = 0.005), and diabetes (β=-0.57, p <0.001), with no difference by race (p = 0.221). Proportions tests confirmed similar biomarker positivity by race (all p ≥0.19). Plasma p-tau217/Aβ42 classified the most cases (AD+/-; Figures 1-3), with significantly fewer undetermined cases (15%) than p-tau217 (31%; χ2(1)=43.26, 95%CI=-0.2 - -0.11, p = 4.8e-11) and Aβ42/Aβ40 (55%; χ2(1)=220.31, 95%CI=-0.44 - -0.34, p = 7.7e-50).

In this real-world dataset, we identified effects of comorbidities (LDL-cholesterol, diabetes, liver, and kidney functioning) on plasma biomarkers. The p-tau217/Aβ42 ratio had low rates of undetermined, and it may help to account for effects of morbidities on plasma levels; still, creatinine remained a significant confound.