Determination of pediatric and adult reference intervals for neurofilament light chain (NfL) in blood and a comparison to other recent studies

Introduction

Background

Certain neurological disorders are characterized by neuroaxonal damage (1). Neurofilaments are cytoskeletal proteins located exclusively in neurons, and upon neuroaxonal damage, neurofilament protein subunits such as neurofilament light chain (NfL), are released into the interstitial fluid, cerebrospinal fluid (CSF), and blood (2,3). NfL has emerged as a promising biomarker that reflects the extent of neuronal degeneration in CSF, although NfL is also released from the central and peripheral nervous systems into the CSF and blood of healthy individuals (4,5). Concentrations of neurofilaments (including NfL) in blood do exhibit a moderately strong correlation with CSF concentrations, but are approximately 40-fold lower (6-8). Additionally, the strength of the correlation of NfL appears to be related to underlying pathology, with patients having central and peripheral nervous system disorders exhibiting a higher correlation between CSF and blood than apparently healthy control patients (8). Advancements in the sensitivity of immunoassay detection methods have made possible the accurate measurement of NfL in serum and plasma, making it a more accessible tool for evaluating neurodegeneration (2,9). Finally, small differences in NfL concentrations have been reported between EDTA plasma and serum. For example, serum concentrations have been reported to be ~10% higher than EDTA plasma in some assays (10).

NfL has been increasingly studied as a biomarker of neuronal damage, differential diagnosis, progression, prognosis, and response to treatment of various neurological diseases in adult populations. NfL can also play a role in therapeutic drug clinical trials for neurodegenerative diseases and has been used as a primary endpoint for amyotrophic lateral sclerosis (ALS) drug approval (11,12). NfL concentrations increase after traumatic brain injury (TBI) and may aid in the diagnosis and prognosis of individuals with TBI (13,14). In the pediatric population, NfL may play a role in patients with early multiple sclerosis (MS) and relapsing-remitting MS for predicting disease progression and prognosis (15-18), evaluation of long-term outcomes (19,20), as well as showing utility for treatment monitoring (21,22). Declining NfL concentrations in response to therapy indicate potential for monitoring the treatment of patients with spinal muscular atrophy (SMA) (23-25). Some studies have suggested the use of NfL to predict outcomes after pediatric cardiac arrest (26,27).

Rationale and knowledge gap

As the association of age and NfL concentration is non-linear, it appears to be important to use either a continuous reference interval or reference intervals with many age partitions (28). In adults, a log-linear relationship of NfL concentration with age has previously been shown to approximate the upper reference limit of serum NfL (29). For pediatric populations, many physiological and developmental changes occur in relatively short time spans, which may alter circulating NfL concentrations. While the use of a continuous reference interval is ideal, it is often difficult for laboratories to obtain a large and diverse group of donors that accurately reflect their patient population. In this case, discrete reference intervals with age partitions are a viable alternative approach. Reference interval evaluation should consider exclusions for confounding factors known to affect analyte concentrations. While less of an issue in pediatric populations, in the absence of neuronal damage or pathology, NfL concentrations may be elevated in individuals presenting with various comorbidities such as chronic kidney disease, glucose dysregulation, history of stroke, and cardiac arrest (16,30,31). Conversely, abnormally high body mass index (BMI) decreases circulating NfL concentrations at an approximate rate of 0.02 pg/mL per unit increase in BMI (16,32). However, the effect of BMI has been shown to have a smaller impact on NfL blood concentrations than other confounders such as age, renal function, hemoglobin A1C, or the presence of diabetes (31).

Reference intervals are important for differentiating potential pathologically elevated concentrations from those observed by healthy individuals (including pediatric/adolescent individuals), and thus require well-characterized sample sets. One example of a promising potential application of pediatric NfL reference intervals is in the area of pediatric-onset multiple sclerosis (POMS), where serum NfL is typically elevated only 2 to 10-fold over matched controls (18,33). Between 3–10% of MS patients present with symptoms at 16 years of age or younger and fewer than 1% at 10 years of age and younger. Pediatric MS guidelines recommend treatment can begin early in the course of the disease (33). Serum NfL has also been shown to have potential utility in monitoring MS treatment and can be predictive of disease progression (18,21). Thus, this provides a disease state example of how an accurate understanding of the age-specific reference interval concentrations is important and can facilitate prognostic progression evaluation and diagnosis in a pediatric population (18,34,35).

A number of recent reports have investigated circulating NfL concentrations versus age in both healthy pediatric and adult populations. In general, circulating blood NfL concentration decreases with age in early pediatric populations (22,23), and increases with age in adult populations (22,23,28,29,36,37). However, differences in study design, reference interval generation, and age stratification are present in these studies. We had previously published 97.5^th percentile reference intervals in adult plasma samples using a quantile regression model using the mid-point for each 10-year age partition (28).

Objective

The objective of this study was to expand on previously published reference intervals to generate both adult and pediatric age-stratified reference intervals with age partitions of ≤5 years using the Quanterix Simoa^® NF Light Advantage Kit assay on the Simoa^® HD-X analyzer. Furthermore, the pediatric reference intervals established in this work were compared to other recently reported pediatric reference intervals (38-44). We present this article in accordance with the STROBE reporting checklist (available at https://jlpm.amegroups.org/article/view/10.21037/jlpm-24-33/rc).

Methods

Participants

Frozen banked donor specimens were gathered from a total of 120 individuals <20 years of age. After the exclusion of 6 outliers (4 with malignancies with potential brain metastases and 2 others with head trauma), the participants included in the final data set had no known history of recent chronic kidney disease [estimated glomerular filtration rate (eGFR) >90 mL/min/1.73 m²], diabetes, neurological conditions, TBI, malignant neoplasm with known or possible brain metastasis, stroke, myocardial infarction, or atrial fibrillation, and had a BMI <30 kg/m². The final study cohort consisted of serum samples from a total of 114 individuals (55 male, 59 female) spanning 6 months through 19 years of age.

Pediatric serum samples

Banked donor pediatric serum samples were used for reference interval determination, as EDTA plasma samples were unavailable for pediatric patients. Specimens were collected in serum separator tubes, and the serum was separated and transferred to polypropylene aliquot tubes within 2 hours, then stored at −80 °C within 72 hours of collection until thawing directly prior to the study testing. Samples were thawed to room temperature, mixed by inversion and vortexing, and centrifuged at 3,500 ×g for 5 minutes directly prior to analysis as part of routine pre-analytic processing for the assay in the clinical laboratory. Samples underwent fewer than 3 freeze/thaw cycles prior to testing, and up to 3 freeze/thaw cycles were shown not to affect analyte concentration based on internal validation studies with ≤4% change from baseline.

Simoa^® NF-light™ Advantage assay

NfL concentrations were measured between 1/11/23 and 1/13/23 using the Simoa^® NF-light™ Advantage Kit version 2 immunoassay (Quanterix catalog number 104073, lot number 503501) per manufacturer instructions. The assay is for quantitative determination of NfL in serum, plasma, or CSF on the Simoa^® HD-X analyzer (Quanterix™, Billerica, MA, USA). Samples were analyzed directly from the aliquot tubes in duplicate and the average concentration was used for analysis, expressed in pg/mL. A lower limit of quantitation of 2.4 pg/mL was utilized for the study based on internal validation. Analytic performance characteristics of this assay have been previously reported (45).

Adult reference intervals

Previously reported EDTA plasma reference interval determinations for adults ≥20 years of age were generated using 1,100 samples from 595 cognitively normal individuals (315 males, 280 females), of which 595 points were randomly selected for each unique individual as previously described (reference correction) (28). The participants included in the final data set also had no known history of recent chronic kidney disease (eGFR >90 mL/min/1.73 m²), diabetes, neurological conditions, TBI, malignant neoplasm with known or possible brain metastasis, stroke, myocardial infarction, or atrial fibrillation, and had a BMI <30 kg/m².

Serum and plasma conversion

Passing-Bablok regression equations, generated using Analyse-it version 6.15 for Microsoft Excel, were used to convert concentrations between plasma and serum in order to establish reference intervals based on both specimen types spanning the clinically relevant range. Matched serum and plasma specimens collected during the same draw were obtained from 39 individuals. Matched samples were analyzed in the same run. The resulting linear regression fit equation was used to convert serum concentrations from this study into corresponding calculated plasma concentrations.

Data analysis

Data from the 114 individuals <20 years of age were combined with data from the previously described 595 individuals ≥20 years of age, using the Simoa^® NF-light™ Advantage Kit version 1 assay (28), yielding a total of 709 unique patient NfL determinations for reference interval analysis. In all, 26 of the 114 individuals included in the additional pediatric study were ≥15 to <20 years of age. Selection of banked serum samples for <20 years of age ensured no individuals with missing data were included in the analysis.

Relationships of the 2.5^th, 50^th, 95^th, and 97.5^th percentiles with age and sex were evaluated using non-parametric quantile regression for each group. A bootstrap re-sampling procedure with replacement with 10,000 replicates was used to determine P values, with <0.05 being considered significant. Model complexity was assessed using fit statistics, which included Bayesian Information Criterion (BIC). Using the relationships determined for each group, smaller 5-year age groups were determined to be appropriate for ages 5 to 85+ with the youngest group split further into <2.5 and 2.5 to <5 years. Upper reference interval limits were calculated using the 97.5% percentile quantile regression at the mid-point of each partition using the anti-log transformation of the data. Reference limits were determined using separate equations for pediatrics (ages 0 to <15 years, n=88) and for adolescents/adults (15 to 85+ years, n=621). Data analysis was performed using the QUANTREG procedure in SAS software (SAS Institute Inc., Cary, NC, USA).

In the analysis of the pediatric data, a potential interaction between sex and a quadratic effect of age on the 50^th percentile was noted in a model that may have been overfitted (high BIC) (P=0.02). No other significant effects of age or sex were observed across other percentiles in pediatrics (all P≥0.11). Among adult donors, age showed a linear association with all extreme percentiles (all P<0.0001), along with a statistically significant cubic effect of age on log₁₀ NfL 50^th percentile (P=0.007). However, simpler models with lower BIC values were preferred. These age-related associations were consistent across all percentiles and were independent of sex (all P≥0.06). To maintain model parsimony, we adopted non-sex specific linear age-effect models for log₁₀ NfL outcomes across all percentiles in both age groups. Data analysis was performed using the QUANTREG procedure in SAS software (SAS Institute Inc.).

Literature review and ethical statement

In order to obtain relevant pediatric reference interval comparisons, the PubMed index was searched for manuscripts using Neurofilament Light chain (and/or NfL) reference interval (and/or reference range), up until 12 March 2024.

The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The use of patient samples from the Mayo Clinic Study of Aging was approved by the Mayo Clinic IRB review board (study number 14-004401), and all other normal donor samples were deemed exempt from IRB review by the Mayo Clinic IRB review board. Written informed consent was obtained for all participants in the Mayo Clinic Study of Aging as well as for normal sample donors and/or their guardians.

Results

NfL concentrations in serum were on average 8.4% higher than in EDTA plasma based on regression analysis. The resulting equation used to transform between sample types was as follows: plasma NfL = 0.907 × serum NfL + 0.028, and R²=0.988 (see Figure 1A). Pediatric NfL serum results were adjusted using this equation for all subsequent plasma reference interval evaluations. Additionally, this equation was used to adjust all calculated adult plasma values into corresponding serum values (See Table 1). Figure 1B shows observed differences between NF-light™ Advantage Kit version 1 and version 2 (~−6% bias) based upon an internal lot-to-lot validation with 32 samples across the analytical measurement range, yielding a Passing-Bablok regression equation of version 2 = 0.939 × version 1 − 0.507, and R²=0.995. Hence, as most manufacturer immunoassay lot preparations vary by as much as ±10%, NfL concentrations generated via version 1 and version 2 NfL assays were considered interchangeable for data analysis in this study.

Figure 1 Passing-Bablok regression analysis for serum versus plasma NfL concentration (A) and NfL kit version 1 versus version 2 (B). (A) Passing-Bablok regression model fit from 39 matched serum and plasma samples and the resulting fit equation used to convert serum to plasma concentrations. The R² of the Passing-Bablok fit was 0.988. (B) Passing-Bablok regression model fit from 32 plasma samples run on Simoa^® NF-light™ Advantage Kit version 2 versus version 1. This yielded a regression equation of version 2 = 0.939 × version 1 − 0.507, with R²=0.995. NfL, neurofilament light chain.

NfL reference intervals appeared to reach a minimum at approximately 15 years of age in this study, before increasing throughout adulthood. Accordingly, two different models were used to fit the reference interval data. A log-linear fit was generated to calculate age-specific reference interval 97.5% percentile upper limits in the <15-year pediatric population [13.35 × 0.9674^{(age in years)}], and a separate log-linear age association [5.90 × 1.0257^{(age in years)}] was generated to calculate reference interval 97.5% percentile upper limits in the ≥15-year population. The ≥15-year population consisted of all available data from both this study and the previously reported study for individuals above 15 years of age (n=621 total). Figure 2A,2B shows the continuous (log-linear) and discrete plasma reference intervals at the 2.5^th, 50^th, 95^th, and 97.5^th percentiles separated by age group. Figure 2C depicts both the <15 and the ≥15-year age percentile fits and associated reference intervals in the same plot.

Figure 2 Plasma NfL concentrations versus age. Best fit log-linear relationships are shown for all percentile measurements and percentile reference intervals as described in Table 1. (A) Pediatric curves and age partition (0 to 15 years). (B) Adult/Adolescent curves and age partitions 15+ years. (C) Adult/adolescent and pediatric curves and age partitions combined. NfL, neurofilament light chain.

Table 1 shows calculated plasma NfL reference limits for both pediatric and adult patients for plasma and serum at the 2.5^th, 50^th, 95^th, and 97.5^th percentiles along with 95% confidence intervals. No differences between males or females were detected for all ages (Wilcoxon rank sum P value: pediatric P=0.07, teenage/adult P=0.44). For pediatric donors, age but not sex was associated with the log₁₀ NfL 50^th percentile (P=0.009). Apart from an interaction between sex and age on the 50^th percentile, no other significant effects of sex or age were observed across other percentiles in pediatrics (all P≥0.11). Among adult donors, age showed an association with the 50^th and all extreme percentiles (all P<0.01). Discrete reference intervals were obtained by taking the estimate for each age group at the midpoint age. To better express changes in NfL reference intervals in different age groups, smaller 5-year age partitions were utilized. The youngest age group was further split into <2.5 years and 2.5 to <5 years.

The log-linear fits indicate that plasma NfL concentrations showed an average decrease of 3.3% per year at the 97.5^th percentile and 4.2% per year at the 50^th percentile for the <15-year age group. In the ≥15-year age group, plasma concentrations increased an estimated 2.6% per year at the 97.5^th percentile, and 2.8% per year at the 50^th percentile. The pediatric and adult fit models predict similar NfL plasma concentrations at age 15 of 8.1 mg/dL and 8.6 pg/mL, respectively for the 97.5% percentile fits indicating that these two independent models matched relatively well at their boundaries. The 50^th percentile fits also exhibited a similar pattern.

Reference interval ranges determined in this study were compared to several other recent NfL pediatric reference interval studies. These studies are described in Table 2. The upper (95^th or 97.5^th) NfL reference limits from all studies that reported upper limits are summarized in Figure 3. While different age ranges and methods were used to determine reference intervals, in general decreasing NfL concentrations with age were observed until 10–15 years of age, and some increases in NfL reference interval concentrations were observed after 12–15 years of age.

Figure 3 95^th or 97.5^th percentile upper limit plasma or serum NfL estimates (from continuous and/or discrete reference intervals) from various studies are plotted. Refer to Table 2 for details regarding each study. NfL, neurofilament light chain.

Discussion

Key findings

The utility of measuring blood NfL concentrations in the pediatric population has been a topic of interest as this non-specific neuronal marker may be useful in the evaluation and monitoring of a variety of neurodegenerative and neuroinflammatory conditions. Some disorders have relatively small differences between pathologic and disease states which increases the importance of having accurate reference interval determination across age ranges. In response to this need, this reference interval study provides a continuous NfL reference interval linking adult and pediatric populations.

The observed differences in NfL concentrations between EDTA plasma and serum presented in this study are in alignment with previous studies which estimate that serum NfL concentrations are roughly an average of 10% higher than in plasma (10,29,45). In this work, NfL concentrations in serum were on average 8.4% higher than in plasma. In one study, the equation generated for plasma-to-serum conversion had a regression fit slope of 1.103, while another study of 299 individuals showed a similar regression fit slope of 1.11 (29,45). This general agreement across studies supported the use of a conversion factor for analyzing data containing both EDTA plasma and serum sample types.

Due to a strong association of NfL concentration with age, care needs to be taken to establish proper age stratifications for reference intervals. In this study, as observed NfL concentration reached an apparent nadir around 15 years of age complicating potential best fits for reference interval determination, reference intervals were evaluated independently for ages 0 to <15 years and ≥15 years. There was good agreement at the boundary of 15 years of age between the fits, suggesting validity in the approach of generating two different fit models. The rate of increase in NfL concentrations at the 97.5^th percentile of 2.6% per year observed in the adult population shown here is similar to the approximately 2.2% and 2.9% increase in concentration per year in adult populations observed in other studies (6,29). The decrease in pediatric NfL concentrations observed in this study, visualized in Figure 2, also matches well with previous reports (22,23).

Strengths and limitations

Overall, our pediatric and adult NfL reference interval results follow the trend observed in other studies regarding the effect of age on NfL concentrations, whereupon initial decreases in NfL concentrations are observed with increasing age in the pediatric population, followed by increases with age in the adult population (22,23,28,29,36,37). In all cases, NfL concentrations reached their intra-study low point between 10 and 15 years of age. The ≤5-year wide reference interval partitions in Figure 2 are an improvement to previously published 10-year wide reference interval partitions and provide more age-specific information to clinicians (28).

Our study is limited by the study population diversity. In our study, the majority of participants represent the population from Olmsted County in southeastern Minnesota (USA). In particular, this population exhibits low diversity likely resulting in a lack of representation of non-white populations. The impact of racially diverse populations on pediatric reference intervals has not been well explored. However, the reference intervals provided by the study of Jin et al. representing a Chinese population did not seem to greatly deviate from the other pediatric interval studies examined in mainly populations of white European ancestry (40). As with any test used clinically, the performance of these reference intervals will be dependent on lot-to-lot variation of the assay which will require a protocol for testing this variation with acceptance criteria for assessment of new lots to maintain acceptable levels of variability.

Comparison with similar research

The results of studies that have estimated age-specific healthy reference intervals for NfL in pediatric populations using the Quanterix Simoa^® NF-Light Advantage Kit are summarized in Table 2 (38-44). Table 2 also highlights potential limitations in comparisons between studies. While overall patterns of NfL reference intervals were similar, there was variation in the absolute values of NfL reference intervals across age groups (see Figure 3). In some cases, especially in younger individuals, reference interval variated as much as 100% at certain ages. The reasons for these discrepancies are not completely understood. As indicated in Table 2, the sample size, specimen type, and reference populations differed between studies. Also, these studies used a variety of statistical modeling methods to show the association between NfL and age and to estimate age-specific reference limits/intervals. Additionally, differing methods were utilized for outlier detection and exclusion. Finally, while in some studies care was taken to ensure possible confounding causes of variation in NfL concentration were excluded, this may not be the case in all studies.

Explanations of findings

While in general NfL pediatric reference interval studies showed consistent trends across the age range, as is shown in Figure 3 there is a large variation in the reference interval age partitions between studies. This variation may limit clinical utility for some comparative applications, and wider age partitions may bias NfL reference interval concentrations. It appears that appropriate age partitions and partition sizes were determined via different methods in different studies. In our previous study, 10-year partitions were used to characterize adult ranges. Due to physician feedback expressing a desire for more precise reference intervals, we have moved to adopt 5-year partitions for NfL reference interval determination.

Lastly, there was variability in analytical factors between the studies presented here that could have had a potential impact/bias on quantitative NfL reference interval determinations. This variability may include factors such as variation in sample type, assay kit versions, or reagent lots. It should be noted, that NfL is not standardized and therefore results may not compare well across multiple assays/platforms (46,47). For example, the Quanterix Simoa reference intervals should not be applied to other analytical methods of NfL determination, as there are potential calibration differences related to the lack of certified (standardized) reference material for NfL.

Implications and actions needed

The establishment of reference intervals in pediatric populations can be challenging (48). Ideally, for the pediatric population, a continuous reference interval may be considered, however many laboratories do not have the resources to carry out studies with a large number of diverse pediatric donors that reflect their testing population. It should be noted that one large study did generate a pediatric Z-score calculator to describe the deviation of serum NfL measurements from reference mean, and this could be another tool to evaluate differences in NfL concentrations on various pediatric and adult disease states. Therefore, the next best option for laboratories is to utilize discrete reference intervals with small age partitions to accurately assess neuroaxonal damage.

Conclusions

This study provides serum and plasma NfL concentrations in a well-characterized pediatric cohort combined with an adult reference cohort. This expands on previous adult plasma NfL data to provide reference intervals from cognitively unimpaired individuals over all ages grouped into narrower age partitions to better distinguish concentration dependency with age. These intervals may aid in interpreting plasma and serum NfL testing for the evaluation of neurological disorders, especially when comparisons to other pediatric reference interval studies are taken into consideration.

Acknowledgments

Funding: None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jlpm.amegroups.org/article/view/10.21037/jlpm-24-33/rc

Data Sharing Statement: https://jlpm.amegroups.org/article/view/10.21037/jlpm-24-33/dss

Peer Review File: Available at https://jlpm.amegroups.org/article/view/10.21037/jlpm-24-33/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jlpm.amegroups.org/article/view/10.21037/jlpm-24-33/coif). J.A.B. serves as an unpaid editorial board member of the Journal of Laboratory and Precision Medicine from October 2023 to September 2025. J.A.B. receives honoraria for lectures and educational events from Roche Diagnostics. A.A.S. receives honoraria for lectures and educational events from Roche Diagnostics, and has participated on Advisory Boards for Fujirebio Diagnostics and Roche Diagnostics. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The use of patient samples from the Mayo Clinic Study of Aging was approved by the Mayo Clinic IRB review board (study number 14-004401), and all other normal donor samples were deemed exempt from IRB review by the Mayo Clinic IRB review board. Written informed consent was obtained for all participants in the Mayo Clinic Study of Aging as well as for normal sample donors and/or their guardians.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Trapp BD, Ransohoff R, Rudick R. Axonal pathology in multiple sclerosis: relationship to neurologic disability. Curr Opin Neurol 1999;12:295-302. [Crossref] [PubMed]
2. Khalil M, Teunissen CE, Otto M, et al. Neurofilaments as biomarkers in neurological disorders. Nat Rev Neurol 2018;14:577-89. [Crossref] [PubMed]
3. Yuan A, Rao MV. Neurofilaments and Neurofilament Proteins in Health and Disease. Cold Spring Harb Perspect Biol 2017;9:a018309. [Crossref] [PubMed]
4. Deisenhammer F, Egg R, Giovannoni G, et al. EFNS guidelines on disease-specific CSF investigations. Eur J Neurol 2009;16:760-70. [Crossref] [PubMed]
5. Zanella I, Blasco H, Filosto M, et al. Editorial: The Impact of Neurofilament Light Chain (NFL) Quantification in Serum and Cerebrospinal Fluid in Neurodegenerative Diseases. Front Neurosci 2022;16:915115. [Crossref] [PubMed]
6. Disanto G, Barro C, Benkert P, et al. Serum Neurofilament light: A biomarker of neuronal damage in multiple sclerosis. Ann Neurol 2017;81:857-70. [Crossref] [PubMed]
7. Halbgebauer S, Steinacker P, Verde F, et al. Comparison of CSF and serum neurofilament light and heavy chain as differential diagnostic biomarkers for ALS. J Neurol Neurosurg Psychiatry 2022;93:68-74. [Crossref] [PubMed]
8. Alagaratnam J, von Widekind S, De Francesco D, et al. Correlation between CSF and blood neurofilament light chain protein: a systematic review and meta-analysis. BMJ Neurol Open 2021;3:e000143. [Crossref] [PubMed]
9. Barro C, Chitnis T, Weiner HL. Blood neurofilament light: a critical review of its application to neurologic disease. Ann Clin Transl Neurol 2020;7:2508-23. [Crossref] [PubMed]
10. Rübsamen N, Willemse EAJ, Leppert D, et al. A Method to Combine Neurofilament Light Measurements From Blood Serum and Plasma in Clinical and Population-Based Studies. Front Neurol 2022;13:894119. [Crossref] [PubMed]
11. Mullard A. NfL makes regulatory debut as neurodegenerative disease biomarker. Nat Rev Drug Discov 2023;22:431-4. [Crossref] [PubMed]
12. Benatar M, Wuu J, Turner MR. Neurofilament light chain in drug development for amyotrophic lateral sclerosis: a critical appraisal. Brain 2023;146:2711-6. [Crossref] [PubMed]
13. Shahim P, Politis A, van der Merwe A, et al. Time course and diagnostic utility of NfL, tau, GFAP, and UCH-L1 in subacute and chronic TBI. Neurology 2020;95:e623-36. [Crossref] [PubMed]
14. Graham NSN, Zimmerman KA, Moro F, et al. Axonal marker neurofilament light predicts long-term outcomes and progressive neurodegeneration after traumatic brain injury. Sci Transl Med 2021;13:eabg9922. [Crossref] [PubMed]
15. Siller N, Kuhle J, Muthuraman M, et al. Serum neurofilament light chain is a biomarker of acute and chronic neuronal damage in early multiple sclerosis. Mult Scler 2019;25:678-86. [Crossref] [PubMed]
16. Benkert P, Meier S, Schaedelin S, et al. Serum neurofilament light chain for individual prognostication of disease activity in people with multiple sclerosis: a retrospective modelling and validation study. Lancet Neurol 2022;21:246-57. [Crossref] [PubMed]
17. Wong YYM, Bruijstens AL, Barro C, et al. Serum neurofilament light chain in pediatric MS and other acquired demyelinating syndromes. Neurology 2019;93:e968-74. [Crossref] [PubMed]
18. Wendel EM, Bertolini A, Kousoulos L, et al. Serum neurofilament light-chain levels in children with monophasic myelin oligodendrocyte glycoprotein-associated disease, multiple sclerosis, and other acquired demyelinating syndrome. Mult Scler 2022;28:1553-61. [Crossref] [PubMed]
19. Thebault S, Abdoli M, Fereshtehnejad SM, et al. Serum neurofilament light chain predicts long term clinical outcomes in multiple sclerosis. Sci Rep 2020;10:10381. [Crossref] [PubMed]
20. Varhaug KN, Barro C, Bjørnevik K, et al. Neurofilament light chain predicts disease activity in relapsing-remitting MS. Neurol Neuroimmunol Neuroinflamm 2018;5:e422. [Crossref] [PubMed]
21. Kuhle J, Chitnis T, Banwell B, et al. Plasma neurofilament light chain in children with relapsing MS receiving teriflunomide or placebo: A post hoc analysis of the randomized TERIKIDS trial. Mult Scler 2023;29:385-94. [Crossref] [PubMed]
22. Reinert MC, Benkert P, Wuerfel J, et al. Serum neurofilament light chain is a useful biomarker in pediatric multiple sclerosis. Neurol Neuroimmunol Neuroinflamm 2020;7:e749. [Crossref] [PubMed]
23. Nitz E, Smitka M, Schallner J, et al. Serum neurofilament light chain in pediatric spinal muscular atrophy patients and healthy children. Ann Clin Transl Neurol 2021;8:2013-24. [Crossref] [PubMed]
24. Alves CRR, Petrillo M, Spellman R, et al. Implications of circulating neurofilaments for spinal muscular atrophy treatment early in life: A case series. Mol Ther Methods Clin Dev 2021;23:524-38. [Crossref] [PubMed]
25. Olsson B, Alberg L, Cullen NC, et al. NFL is a marker of treatment response in children with SMA treated with nusinersen. J Neurol 2019;266:2129-36. [Crossref] [PubMed]
26. Kirschen MP, Yehya N, Graham K, et al. Circulating Neurofilament Light Chain Is Associated With Survival After Pediatric Cardiac Arrest. Pediatr Crit Care Med 2020;21:656-61. [Crossref] [PubMed]
27. Fink EL, Kochanek PM, Panigrahy A, et al. Association of Blood-Based Brain Injury Biomarker Concentrations With Outcomes After Pediatric Cardiac Arrest. JAMA Netw Open 2022;5:e2230518. [Crossref] [PubMed]
28. Bornhorst JA, Figdore D, Campbell MR, et al. Plasma neurofilament light chain (NfL) reference interval determination in an Age-stratified cognitively unimpaired cohort. Clin Chim Acta 2022;535:153-6. [Crossref] [PubMed]
29. Hviid CVB, Knudsen CS, Parkner T. Reference interval and preanalytical properties of serum neurofilament light chain in Scandinavian adults. Scand J Clin Lab Invest 2020;80:291-5. [Crossref] [PubMed]
30. Blennow Nordström E, Lilja G, Ullén S, et al. Serum neurofilament light levels are correlated to long-term neurocognitive outcome measures after cardiac arrest. Brain Inj 2022;36:800-9. [Crossref] [PubMed]
31. Fitzgerald KC, Sotirchos ES, Smith MD, et al. Contributors to Serum NfL Levels in People without Neurologic Disease. Ann Neurol 2022;92:688-98. [Crossref] [PubMed]
32. Manouchehrinia A, Piehl F, Hillert J, et al. Confounding effect of blood volume and body mass index on blood neurofilament light chain levels. Ann Clin Transl Neurol 2020;7:139-43. [Crossref] [PubMed]
33. Alroughani R, Boyko A. Pediatric multiple sclerosis: a review. BMC Neurol 2018;18:27. [Crossref] [PubMed]
34. Jakimovski D, Awan S, Eckert SP, et al. Multiple Sclerosis in Children: Differential Diagnosis, Prognosis, and Disease-Modifying Treatment. CNS Drugs 2022;36:45-59. [Crossref] [PubMed]
35. Thebault S, Bar-Or A, Banwell B. NfL is ready for translation into paediatrics. Lancet Neurol 2023;22:774-6. [Crossref] [PubMed]
36. Simrén J, Andreasson U, Gobom J, et al. Establishment of reference values for plasma neurofilament light based on healthy individuals aged 5-90 years. Brain Commun 2022;4:fcac174. [Crossref] [PubMed]
37. Khalil M, Pirpamer L, Hofer E, et al. Serum neurofilament light levels in normal aging and their association with morphologic brain changes. Nat Commun 2020;11:812. [Crossref] [PubMed]
38. Geis T, Gutzeit S, Fouzas S, et al. Serum Neurofilament light chain (NfL) levels in children with and without neurologic diseases. Eur J Paediatr Neurol 2023;45:9-13. [Crossref] [PubMed]
39. Abdelhak A, Petermeier F, Benkert P, et al. Serum neurofilament light chain reference database for individual application in paediatric care: a retrospective modelling and validation study. Lancet Neurol 2023;22:826-33. [Crossref] [PubMed]
40. Jin J, Cui Y, Hong Y, et al. Reference values for plasma neurofilament light chain in healthy Chinese children. Clin Chem Lab Med 2022;60:e10-2. [Crossref] [PubMed]
41. Stukas S, Cooper J, Higgins V, et al. Pediatric reference intervals for serum neurofilament light and glial fibrillary acidic protein using the Canadian Laboratory Initiative on Pediatric Reference Intervals (CALIPER) cohort. Clin Chem Lab Med 2024;62:698-705. [Crossref] [PubMed]
42. Cooper JG, Stukas S, Ghodsi M, et al. Age specific reference intervals for plasma biomarkers of neurodegeneration and neurotrauma in a Canadian population. Clin Biochem 2023;121-122:110680. [Crossref] [PubMed]
43. Schjørring ME, Parkner T, Knudsen CS, et al. Neurofilament light chain: serum reference intervals in Danish children aged 0-17 years. Scand J Clin Lab Invest 2023;83:403-7. [Crossref] [PubMed]
44. Bayoumy S, Verberk IMW, Vermunt L, et al. Neurofilament light protein as a biomarker for spinal muscular atrophy: a review and reference ranges. Clin Chem Lab Med 2024;62:1252-65. [Crossref] [PubMed]
45. Altmann P, Ponleitner M, Rommer PS, et al. Seven day pre-analytical stability of serum and plasma neurofilament light chain. Sci Rep 2021;11:11034. [Crossref] [PubMed]
46. Gauthier A, Viel S, Perret M, et al. Comparison of Simoa(TM) and Ella(TM) to assess serum neurofilament-light chain in multiple sclerosis. Ann Clin Transl Neurol 2021;8:1141-50. [Crossref] [PubMed]
47. Kuhle J, Barro C, Andreasson U, et al. Comparison of three analytical platforms for quantification of the neurofilament light chain in blood samples: ELISA, electrochemiluminescence immunoassay and Simoa. Clin Chem Lab Med 2016;54:1655-61. [Crossref] [PubMed]
48. Hoq M, Matthews S, Donath S, et al. Paediatric Reference Intervals: Current Status, Gaps, Challenges and Future Considerations. Clin Biochem Rev 2020;41:43-52. [PubMed]