Comparative Analysis of SiMoA and Ella Immunoassay Platforms for Measuring Serum Neurofilament Light Chain Levels in ATTRv With Polyneuropathy and Presymptomatic Carriers

Abstract

Background: Neurofilament light chains (NfL) represent reliable serum biomarkers of neuroaxonal injury. Due to their low serum levels, precise detection methods are critical. This study aimed to scrutinize the comparability of two techniques: Single Molecule Array (SiMoA) and Ella automated immunoassay, analyzing serum NfL levels in ATTRv presymptomatic subjects and polyneuropathy patients.

Methods: Blood samples were processed and analyzed using commercial Ella and SiMoA kits. Statistical analysis included the Wilcoxon signed-rank test, Spearman correlation, Bland-Altman, and Passing-Bablok regression. ANCOVA models were used to compare NfL levels between cohorts.

Results: The study measured serum NfL levels in 55 symptomatic and 55 presymptomatic ATTRv subjects. Median NfL concentrations were significantly higher with Ella (median 27.5 pg/mL) than SiMoA (median 15.9 pg/mL). Both methods showed a strong positive correlation (r = 0.8, p < 0.001), but Ella overestimated NfL by 42%. Bland-Altman analysis revealed a mean bias of 15.4 pg/mL, with limits of agreement between -41.1 and 72.0 pg/mL. The slope of the Passing-Bablok regression line was 0.58, and the intercept was 3.48 pg/mL, suggesting that the Ella platform tends to overestimate NfL concentrations compared to the SiMoA platform, especially at higher concentrations. Both methods effectively distinguished presymptomatic from symptomatic patients (p < 0.001 for both).

Conclusions: Our findings underscore that both platforms are effective in measuring serum NfL, with Ella consistently overestimating, especially at higher concentrations. The difference between the two platforms must be taken into account when deeming the concentrations as pathological or normal, as well as when conducting longitudinal studies.

Keywords: SiMoA; biomarker; ella; method comparison; neurofilament light chain.

FIGURE 1

Boxplots and histograms with density curves. (A) Box plots express the first (Q1) and third (Q3) quartiles by the upper and lower horizontal lines in a rectangular box, in which there is a horizontal line showing the median. The whiskers extend upwards and downwards to the highest or lowest observation within the upper (Q3 + 1.5 × IQR) and lower (Q1–1.5 × IQR) limits. p values indicate statistical significance between the different groups. (B) histograms with density curves showing the comparison of NfL concentrations distribution measured by SiMoA and ELLA methods.

FIGURE 2

Bland–Altman plots illustrating the agreement between the two measurement methods. The X‐axis represents the mean values of the two methods, while the Y‐axis represents their differences. The blue central line indicates the mean bias, the upper and lower dashed lines correspond to the limits of agreement (±1.96 SD).

FIGURE 3

Passing Bablock regression plot comparing NfL measurements between Ella and SiMoA methods. The x‐axis represents NfL concentrations measured by ELLA (pg/ml), and the y‐axis represents NfL concentrations measured by SiMoA (pg/ml). The blue line indicates the linear regression fit, with the shaded area representing the confidence interval. The equation of the regression line is y = 3.4 + 0.58x, and the sample size is n = 110.

FIGURE 4

Comparison of serum NfL levels between presymptomatic subjects and symptomatic ATTRv patients using both Ella and SiMoA.