Bornhorst, Joshua

Abstract INTRODUCTION Plasma phosphorylated tau at threonine 217 (p‐tau217) has emerged as one of the most promising blood‐based biomarkers for Alzheimer's disease (AD). While rare, heterophilic antibodies (HAb) are a persistent potential confounding factor in immunoassays. METHODS Potential HAb interference in the Lumipulse G pTau217 assay in samples exhibiting concentrations > 10 pg/mL were investigated. Samples were subjected to HAb blocking reagent (HBT), and in some cases, polyethylene glycol (PEG) precipitation and serial dilutions. RESULTS In 14 of the 15 suspected HAb cases, HBT treatment greatly reduced measured p‐tau217 concentrations. and in one of three specimens selected for further investigation, reduced Aβ42 concentrations PEG precipitation in the three selected samples also reduced p‐tau217 concentrations, while serial dilution yielded mixed effects. Control specimens were unaffected by sample treatment or dilutions. DISCUSSION HAb may result in falsely elevated p‐tau217 and p‐tau217/Aβ42 ratio. HAb interference should be considered in cases of unusually high p‐tau217 concentrations prior to clinical interpretation. Highlights Potential heterophile antibody (HAb) interference in the Lumipulse p‐tau217 immunoassay was investigated. Investigation was performed using HAb blocking reagent, and in some cases also using PEG precipitation . Patients with p‐tau217 concentrations > 10 pg/mL exhibited positive HAb interference in 14 of 15 cases. HAb interference can lead to falsely positive p‐tau217/Aβ42 ratios.

Abstract Background The polymorphic APOE gene is a susceptibility gene for Alzheimer's disease (AD). The ε4 allele is associated with increased risk for AD, particularly late‐onset disease, in a dose‐dependent manner. Additionally, homozygous ε4/ε4 individuals have increased risk of adverse events when undergoing amyloid lowering treatments. APOE genotyping is considered the gold standard for determination of ApoE4 zygosity. Recently, proteotype assays for ApoE4 have become available for high‐throughput immunoassay analyzers. These assays utilize the same specimen type as AD blood biomarkers and can potentially offer improved turnaround times compared to genotyping. In this study, we compare the performance of two automated ApoE4 proteotype research use only (RUO) immunoassays against APOE genotyping. Method EDTA‐plasma samples ( n = 65) from individuals undergoing ApoE PCR‐based genotyping for clinical purposes were evaluated. Samples were tested with the Beckman Coulter APOE ε4 RUO assay on the Access 2 and DXI 9000 instruments (Beckman Coulter, Inc), which provides algorithm calculated results for determining ApoE4 zygosity. Manufacturer generated data from 300 genotyped samples was used to calculate estimated cut‐points for ApoE4 zygosity for this study with results <0.55 classified as no E4, ≥0.55 to <4.55 as heterozygous E4, and ≥4.55 as homozygous E4. Samples were also tested with the Lumipulse G ApoE4 and Pan‐ApoE RUO assays on the Fujirebio Lumipulse G1200 analyzer. The ratio of ApoE4/Pan‐ApoE was utilized for determining zygosity with results <5% classified as no E4, ≥5% to <75% as heterozygous E4, and ≥75% as homozygous E4, as listed in the manufacturer IFU. Result APOE genotype distributions were (n, %): ε3ε4 (30, 46%), ε3ε3 (18, 28%), ε4ε4 (12, 18%), ε2ε3 (3, 5%), ε2ε4 (2, 3%). ApoE4 zygosity was categorized as no ε4 (21, 32%), heterozygous ε4 (32, 49%), or homozygous ε4 (12, 19%). The Beckman Coulter APOE ε4 RUO assay classified 65/65 (100%) patients correctly using manufacturer generated cut‐points on both instruments. The Lumipulse G ApoE4 and Pan‐ApoE RUO assays classified 61/65 (94%) patients correctly using the manufacturer listed cut‐points. Conclusion ApoE4 proteotype immunoassays may represent simplified and more accessible testing alternatives to genotyping for the assessment of ApoE4 zygosity in individuals being considered for amyloid lowering treatments.

Abstract Background Chronic kidney disease (CKD) is associated with increased blood‐based biomarker concentrations, potentially confounding their utility in Alzheimer's disease (AD) evaluation. While plasma phosphorylated tau217 ( p ‐tau217) is elevated in the presence of amyloid related pathology, amyloid beta 1‐42 (Aβ42) is decreased. We investigated the association of plasma p ‐tau217, non‐phosphorylated tau217 (np‐tau217), Aβ42, Aβ40, as well as the Aβ42/Aβ40 and p ‐tau217/Aβ42 ratios, versus decreased estimated glomerular filtration rate (eGFR in mL/min/1.73 m 2 ) in individuals without amyloid pathology. Method This study included participants with CKD stages 1‐2 (eGFR 60‐98, n = 50), and stages 3‐4 (eGFR 25‐59, n = 33), who were Pittsburgh 11 C‐Compound B amyloid‐PET negative (Centiloid of < 25). Plasma p ‐tau217, np‐tau217, Aβ42, and Aβ40 were measured by immunoprecipitation mass spectrometry (C 2 N Diagnostics). %p‐tau217 [( p ‐tau217/np‐tau217) x100], Aβ42/Aβ40 ratio, and p ‐tau217/Aβ42 ratio were calculated. Log‐Log (power function) best‐fit regression analysis was used to quantitatively predict effects of changes in eGFR (2021 CKD‐EPI equation) versus each single analyte or ratio (Figure 1). Result Selected best‐fit analyte equations versus eGFR are shown in Table 1. The predicted percent increase of p ‐tau217 as eGFR decreases from 60 to 45 was 52% (95% CI: 30–78%). Significantly smaller increases of 16% were predicted for Aβ42 (95% CI: 12–21%), and 19% for Aβ40 (95% CI: 16–23%) over the same eGFR range. The best‐fit predicted increase for the p ‐tau217/Aβ42 ratio and %p‐tau217 as eGFR decreases from 60 to 45 was 31% (95% CI: 12–53%), and 19% (95% CI: 2–38%), respectively. While not recommended for assessment of amyloid pathology, the Aβ42/Aβ40 ratio did not exhibit a predicted increase (‐2.3% decrease, 95% CI: ‐5.2–0.6%) versus decreasing eGFR from 60 to 45. Conclusion The use of either %p‐tau217 or the p ‐tau217/Aβ42 ratio (to a lesser degree) reduced the confounding effects of decreasing eGFR as compared to p ‐tau217 alone. Aβ42 and Aβ40 exhibited similar reduced predicted increases versus decreasing eGFR as compared to p ‐tau217. Relative to the predicted effects of decreasing eGFR on p ‐tau217 measurements, the p ‐tau217/Aβ42 ratio relative increase was reduced by 40%, while the relative increase was reduced by 63% for %p‐tau217 measurements.

Abstract Background Clinically available plasma p ‐tau217 assays may be utilized in the determination of eligibility for amyloid‐lowering therapies. Our institution recently introduced a plasma p ‐tau217 assay in clinical practice using a two‐cutpoint approach that optimizes the accuracy while minimizing false positive risk and categorizing ≤20% of results as intermediate. In this study, we prospectively evaluate the performance of a plasma p ‐tau217 assay for detection of amyloid pathology using these predefined cutpoints. Method Patients recruited were being considered for lecanemab therapy at a tertiary care subspecialty clinic. Plasma p ‐tau217 was measured using the clinically available Fujirebio Lumipulse p ‐tau217 assay at Mayo Clinic, and results (pg/mL) were classified as either negative (≤0.185), intermediate (0.186–0.324) or positive (≥0.325). Amyloid pathology was determined by amyloid‐PET and/or CSF p ‐tau181/Aβ42. Result Ninety‐three patients were recruited between November 2023 and December 2024. Of these, 49 underwent amyloid‐PET, 4 had CSF p ‐tau181/Aβ42 measurements, and 40 had both PET and CSF results (with 3/40 discordant cases), for use in the assessment of amyloid pathology. The three discordant cases were considered amyloid positive for purposes of plasma p ‐tau217 comparison. Overall amyloid positivity was 90%. Plasma p ‐tau217 results were positive in 83% (77/93), negative in 6% (6/93), and intermediate in 11% (10/93) of patients. An elevated p ‐tau217 predicted the presence of amyloid positivity with a diagnostic accuracy of 96% (95% CI 90% − 99%). In the intermediate range, 80% of patients were positive for amyloid pathology. In patients with a definitive p ‐tau217 result (positive or negative), the positive and negative predictive values were 97% and 83%. There were three patients with discordant results: one PET+/p‐tau217‐, one PET‐/p‐tau217+, and one CSF‐/p‐tau217+. Clinical presentation of these discordant cases was examined, and relevant findings will be discussed. Conclusion The Lumipulse plasma p ‐tau217 assay exhibited acceptable diagnostic accuracy for the determination of amyloid pathology when compared to either amyloid‐PET or CSF p ‐tau181/Aβ42. This prospective study confirms the utility a two‐cutpoint approach for interpreting plasma p ‐tau217 for the assessment of amyloid pathology eligibility for amyloid‐lowering therapies in a heterogenous clinical cohort.

Abstract Background Alzheimer's disease (AD) blood biomarkers (BBMs) are increasingly used in clinical trials and clinical practice. However, widespread adoption of BBMs requires further understanding of factors that might influence the interpretation of these biomarkers which would allow for the development of standardized sample collection protocols. For example, studies of the effect of fasting on AD BBM concentrations have yielded inconsistent findings. In this study, we evaluated plasma concentrations of amyloid‐beta(Aβ) 42, Aβ40, phosphorylated Tau ( p ‐tau) 181, p ‐tau217, and neurofilament light chain (NfL) in cognitively normal individuals under fasting and non‐fasting conditions. Method EDTA‐plasma was collected from healthy donors ( n = 14; age >55yrs old) two weeks apart, at the same time of day. The first sample collection was under fasting conditions in which donors did not eat or drink (except water) for at least 12 hours prior to collection. The second sample collection was under non‐fasting conditions in which donors were instructed to eat a meal in the morning, approximately half an hour prior to collection. Plasma Aβ42, Aβ40, p ‐tau181, p ‐tau217, and NfL concentrations were measured on the Fujirebio Lumipulse G1200 analyzer. Wilcoxon signed‐rank test was used to compare values between the fasting and non‐fasting results. Spearman's rank correlation was used to assess biomarker correlation between fasting status. Result Moderate to strong correlation was observed between the fasting and non‐fasting measurements: p ‐tau217 (r s : 0.86), p ‐tau181 (r s : 0.89), NfL (r s : 0.94), p ‐tau217/Aβ42 (r s : 0.80), Aβ42/40 (r s : 0.66), Aβ42 (r s : 0.77), and Aβ40 (r s : 0.92). Average percent difference between the 2 conditions was: p ‐tau217 27%, p ‐tau181 6%, NfL 9%, p ‐tau217/ Aβ42 25%, Aβ42/40 4%, Aβ42 2%, and Aβ40 ‐6%. Statistically significant differences ( p ≤ 0.05) between fasting and non‐fasting measurements were observed for p ‐tau217, NfL, p ‐tau217/Aβ42, Aβ42/Aβ40, and Aβ42; but not for Aβ40 or p ‐tau181. Conclusion This data suggests that for some AD BBMs, there may be statistically significant differences in concentrations of samples collected in fasting versus non‐fasting conditions. However, further studies are needed to determine if the observed differences may affect the clinical interpretation of these BBMs in individuals with amyloid related pathology.

Abstract Background Anti‐amyloid therapy trials have reported changes in some Alzheimer's disease (AD) blood biomarkers (BBMs) suggesting that these BBMs may be useful minimally invasive measures of amyloid clearance and treatment outcomes. However, a better understanding of how AD BBMs changes at the individual level reflect treatment response in relation to other relevant clinical endpoints is necessary before they can be adopted for treatment monitoring. Here, several AD BBMs were assessed longitudinally in patients undergoing lecanemab therapy. Method Patients undergoing lecanemab therapy at Mayo Clinic, Rochester, MN were recruited to participate in this study. Patients were asked to provide an EDTA‐plasma sample before treatment initiation during the first infusion visit and thereafter at 3‐, 6‐, 12‐, and 18 months post‐treatment. p ‐tau217, p ‐tau181, GFAP, NfL, Aβ42, Aβ40, Aβ42/40, and p ‐tau217/Aβ42 measurements were obtained using Fujirebio Lumipulse assays. Biomarker median differences were assessed between all time points. Patients were grouped into three categories: a decreased biomarker (median decrease of at least 10%), an increased biomarker (median increase of at least 10%), and a stable biomarker (median change < +/−10%.) Biomarker data up to 6 months after treatment is presented. Result Of forty‐one patients enrolled since November 2023, twenty had time points up to 6 months. None of the biomarkers showed a statistically significant median change from baseline at 3 months ( p >0.05). At 6 months, only Aβ42/40 showed a statistically significant median change (decrease) between 0 and 6 months ( n = 20, p = 0.0058). Table 1 shows patients grouped by median biomarker changes from baseline to 6 months. GFAP, p ‐tau217, and Aβ42/40 exhibited the greatest number of patients with decreased biomarker concentrations (80%, 60%, and 60% of patients with median decreases of ‐25%, ‐26%, and ‐18% respectively), followed by p ‐tau181 (50% of patients; median decrease ‐22%), p ‐tau217/Aβ42 (45% of patients; median decrease ‐40%) and Aβ42 (45% of patients; median decrease ‐18%). None of the patients showed a decreased NfL or Aβ40 concentration. Conclusion Preliminarily analysis revealed that GFAP, p ‐tau217, and Aβ42/40 had the most frequent post‐lecanemab biomarker decreases. Additional sample collection is ongoing to assess the association of AD BBM changes with Amyloid PET over time.

Abstract Background Cognitive impairment (CI) has diverse neurological etiologies, including Alzheimer’s Disease (AD), non-degenerative (ND) conditions, and cerebrospinal fluid (CSF) dynamic disorders, such as normal pressure hydrocephalus (NPH). The etiology of CI may be different to diagnose due to the overlap of non-specific symptoms. Various CSF biomarkers, such as amyloid beta (Aβ) 42, Aβ40, total Tau (t-Tau), and phosphorylated Tau 181 (p-Tau181), have been evaluated for their diagnostic utility in identifying the underlying cause for CI. Previous studies have suggested an isolated abnormal Aβ42 levels may be indicative of NPH in the appropriate clinical context. This study aims to further explore the clinical utility of AD-related CSF biomarkers to distinguish NPH from AD and ND causes of CI. Methods 240 patients were chart reviewed and categorized as either AD (n = 124), ND (n = 68), or NPH (n = 47) based on the etiologies of CI. Concentrations of Aβ40, Aβ42, t-Tau, p-Tau181 were measured in CSF (Cobas e601, Roche). Receiver operating characteristic (ROC) curves were plotted and optimal Youden cutoffs and areas under curve (AUCs) were calculated for each biomarker, and for selected ratios of biomarker combinations, for their ability to differentiate NPH from either AD or ND. Additionally, qualitative (abnormal/normal) result patterns for Aβ42, t-Tau, p-Tau181, and p-Tau181/Aβ42 ratio were reviewed for each patient, using established cut-offs for identifying AD (Aβ42≤1026 pg/mL, t-Tau&gt;238 pg/mL, p-Tau181&gt;21.7 pg/mL, p-Tau181/Aβ42&gt;0.023). Results p-Tau181/Aβ42 ratio demonstrated one of the highest AUCs (0.931) to separate NPH from AD (sensitivity=84.8%, specificity= 91.9%), and Aβ42 showed the highest AUC (0.856) to separate NPH from ND (sensitivity=71.6%, specificity=89.7%). When using previously established AD cut-offs, the combination of an abnormally low Aβ42 along with a normal p-Tau181/Aβ42 ratio yielded a sensitivity of 40.4% and a specificity of 96.4% in distinguishing NPH from other CI etiologies in this cohort. In contrast, abnormal results for both Aβ42 and p-Tau181/Aβ42 ratio had a sensitivity of 89.5% and a specificity of 87.0% in identifying AD, while normal results for both biomarkers had a sensitivity of 91.2% and a specificity of 90.1% in identifying ND. Incorporating the qualitative results for t-Tau and p-Tau181 into the evaluation did not enhance the diagnostic performance for distinguishing NPH, AD or ND in this cohort. Conclusion ROC analysis indicated that p-Tau181/Aβ42 and Aβ42 may help differentiate NPH from AD and ND, respectively. However, the combination of an abnormally low Aβ42 and a normal p-Tau181/Aβ42 ratio, using current AD cut-offs, demonstrated a lower sensitivity but high specificity in distinguishing NPH from the other CI etiologies in this cohort, suggesting this result pattern may be used for NPH rule-in in patients with CI.

Abstract Peanut allergy is a leading cause of food-induced allergy (prevalence of ∼1%). The diagnosis relies on evaluating clinical symptoms consistent with peanut exposure, supported by the detection of total peanut specific IgE (sIgE) and peanut component IgE antibodies (Ara h1, Ara h2, Ara h3, Ara h6, Ara h8, Ara h9 and Bet v2) through serum or skin testing. However, sensitization patterns across different ages and regions in the United States remain largely unknown. In this study, we investigated regional and demographic patterns of peanut component sensitization in a large U.S. population tested for suspected peanut allergy. Retrospective data were collected from 13,702 individuals tested at Mayo Clinic Laboratories. sIgEs were measured using the ImmunoCAP system (Thermo Fisher Scientific). Samples with detectable total peanut sIgE (≥0.1 kU/L) were reflexed to testing for seven peanut component IgEs. Statistical analyses including linear regression and correlation matrix analysis were conducted using R Studio. Regional differences were assessed using care provider zip code information. Among the study population, 92.0% (12,604 of 13,702) had detectable total peanut sIgE, with the Western U.S. region exhibiting the highest detectable rate (95.6%), and the Southeast the lowest (85.6%) (p &lt; 0.001). On average, 3.38 different component IgEs were detectable per person with a detectable total peanut sIgE; 7.1% (892) had no detectable component IgEs, possibly due to antibodies against other peanut components. Correlation analysis revealed strong associations between Ara h2 and Ara h6 (r = 0.94), with moderate correlations observed between Ara h2, Ara h3, and Ara h6 to Ara h1 (r ranging from 0.72 to 0.77). Age-stratified analysis indicated higher total peanut sIgE detectable rates in children and adolescents (95.2%, ≤18 years) compared to adults (76.5%, &gt;18 years). Interestingly, adults were more likely than children to have negative results for all component IgEs. Sensitization rates to different peanut components varied, with Ara h2 (77.5%) and Ara h6 (73.2%) being the most frequently detected, followed by Ara h1 (56%), and Ara h3 (47.3%). Lower detectable rates were observed for Ara h8, Ara h9, and Bet v2 (34.8%, 26.1% and 22.7%, respectively). Regional analysis showed consistently high detectable rates for Ara h2 and Ara h6 (&gt;70%) across most areas (p &lt; 0.001) with slightly lower rates in the Southwest (&lt;63%). Bet v2, despite its overall low prevalence (&lt;24%), had a relatively higher detectable rate in the Southwest (29%). This study provides valuable insights into potential demographic and geographic factors influencing peanut allergy sensitization. Our study demonstrates that peanut sensitization patterns vary by age and geographic location. Children and adolescents exhibit higher detectable rates for total peanut sIgE and component IgEs compared to adults, with Ara h2 and Ara h6 as the most frequently detected and highly correlated components.

Abstract Background Alzheimer’s disease (AD) cerebrospinal fluid (CSF) biomarkers, including the Aß42/40 and p-tau181/Aß42 ratios, are used in clinical practice to detect the presence of amyloid pathology for the diagnosis of AD. However, in some instances, discrepancies between Aß42/40 and p-tau181/Aß42 are observed. Such discrepancies may introduce uncertainties in the clinical management of patients presenting with cognitive decline. Identifying the underlying causes of these discrepancies and determining which biomarker abnormalities better predict disease progression is crucial to enhancing confidence in the use of these CSF biomarkers for the diagnosis of AD. This study aims to investigate the discordance between the Aß42/40 and p-tau181/Aß42 ratios, evaluate the frequency of these discrepancies, and identify potential causes. Methods Data from 958 individuals who had both CSF Aß42/40 and p-tau181/Aß42 tested at Mayo Clinic Laboratories between 2022 and 2024 and where the tests were ordered in CSF collected during the same lumbar puncture procedure were included. Cases with an inadequate sample collection, which could cause a false decrease in Aß42 concentrations, were excluded from the analysis. Aß42/40 was measured using the Fujirebio LUMIPULSE assays and reported as negative, likely positive, or positive. For this analysis, likely positive and positive results were combined and considered as positive (&lt;0.072). P-tau181/Aß42 was measured using the Roche Elecsys assays and above 0.028 was considered positive. Statistical analyses were conducted using R Studio. Results Aß42/40 was positive in 69.1% of cases (n=661), while p-tau181/Aß42 was positive in 62.1% (n=594). There were 8.0% discordant cases (n=77). Most frequently, the discordant cases had an abnormal Aß42/40 with a normal p-tau181/Aß42 (Aß42/40+/p-tau181/Aß42-; n=72, 94%). Compared to the concordant Aß42/40+/p-tau181/Aß42+ group, the discordant Aß42/40+/p-tau181/Aß42- group showed significantly higher Aß42 concentrations (p &lt;0.001, median [pg/mL]: 878.5 vs 587.0, respectively); whereas p-tau181 concentrations were significantly lower (p &lt;0.001, median [pg/mL]: 19.3 vs 32.1, respectively). Among the Aß42/40+/p-tau181/Aß42- group, 30 cases exhibited abnormally low Aß42 and normal p-tau181, possibly reflecting early-stage AD. There were 41 cases with a normal Aß42 concentration despite an abnormal Aß42/40, possibly reflecting an overall higher production of Aß peptides resulting in an increased Aß40 peptide (median [pg/mL]: 12627 compared to 9487 in the low Aß42 and normal p-tau181 cases (n=30); p &lt;0.001). Of these 41, 19 showed normal Aß42 but elevated p-tau181 concentrations where the use of Aß42/40 compensated for the overall higher production of Aß peptides, resulting in an abnormal ratio. In contrast, the p-tau181/Aß42 ratio was not able to normalize for these differences, leading to a normal ratio. Conclusion While overall concordance was 92.0%, our findings suggest that discrepancies between CSF Aß42/40 and p-Tau181/Aß42 are more often due to the presence of an abnormal Aß42/40 and a normal p-Tau181/Aß42. Two potential explanations for these discrepancies are early-stage AD or higher production of Aß peptides in some individuals. In the latter, differences in amyloid production would be normalized by ratios of the same biomarker (i.e. Aß42/40) but not by ratios of different biomarkers (i.e. p-Tau181/Aß42).

Abstract Aims Blood biomarkers (BBMs) are promising minimally invasive tools for the evaluation of Alzheimer’s disease (AD). However, recent studies have demonstrated that comorbidities, such as severe chronic kidney disease (CKD), may elevate circulating concentrations of various BBMs including amyloid-ß (Aß) and phosphorylated tau proteins (p-tau). Previous work has found that the effects of CKD on BBM plasma concentrations could be partially mitigated through use of biomarker ratios (e.g., the proportion of p-tau217 to non-phosphorylated tau217 (np-tau217)). In this work, we quantitatively evaluate how different combinations of BBM ratios and single biomarkers are affected in the context of decreased kidney function. Methods Participants (n=83, &gt;57 years of age) with CKD stages 1-2 (eGFR 60-98, n = 50), and stages 3-4 (eGFR 25-59, n = 33) and without amyloid pathology (A-) were included. eGFR (mL/min/1.73 m2) was calculated using the 2021 CKD-EPI equation based on serum-paired creatinine measurements. Plasma p-tau217, np-tau217, p-tau181, np-tau181, Aß42, and Aß40 were measured by mass spectrometry (MS) (C2N Diagnostics). %p-tau217 [(p-tau217/np-tau217) x 100], %p-tau181 [(p-tau181/np-tau181) x 100], Aß42/Aß40 ratio, and p-tau217/Aß42 ratio were calculated. Log-Log (power function) best-fit regression analysis was used to quantitatively predict the relationship of BBM changes as a function of eGFR. Results Median concentrations of p-tau217, np-tau217, p-tau181, np-tau181, Aß42, and Aß40 were all significantly elevated in individuals with eGFR &lt;60 mL/min/1.73 m2 compared to those with eGFR &gt; or =60 (all p &lt; 0.05). There were no differences in the %p-tau217 and Aß42/Aß40 median values between these two groups (eGFR &lt;60 versus &gt; or =60) (p &gt; 0.05); whereas the proportions %p-tau181 and p-tau217/Aß42 median values were higher in the eGFR &gt; or =60 group versus the &lt;60 subset. Observed best-fit analyte regression equations of eGFR versus BBM concentrations predict that an eGFR decrease from 60 to 45 results in p-tau217 and p-tau181 increases of 52% (95% confidence interval (CI): 30–78%) and 40% (95% CI: 29–53%), respectively. A 16% (95% CI: 12–21%), and a 19% (95% CI: 16–23%) increase was predicted in response to the same eGFR decline for Aß42 and Aß40. Furthermore, increases of 19% (95% CI: 2–38%) for %p-tau217, 6% (95% CI: -0.02–13%) for %p-tau181 and 31% (95% CI: 12–53%) for p-tau217/Aß42 were predicted as eGFR declined from 60 to 45, while a minor decrease of 2.3% (95% CI: -5.2–0.6%) was predicted for Aß42/Aß40. Conclusions: Reduction in eGFR is associated with significant elevations in plasma concentrations of p-tau217, p-tau181, Aß42, and Aß40, which may affect the interpretations of these biomarkers. However, the use of %p-tau217, %p-tau181, or p-tau217/Aß42 could partially attenuate this effect. Although the Aß42/Aß40 ratio is not considered an effective diagnostic BBM for AD, this ratio was relatively unaffected by CKD. For example, in comparison to p-tau217 alone, using %p-tau217 or p-tau217/Aß42, the relative increase in analyte values associated with decreased eGFR was reduced by 63% and 40%, respectively. These findings provide a better understanding of the effect of reduced eGFR on AD BBM interpretation in the presence of CKD.