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Cited by 27Clinical Laboratory Practices and Quality ControlSkin and Cellular Biology ResearchMultiple Sclerosis Research Studies

A Method to Combine Neurofilament Light Measurements From Blood Serum and Plasma in Clinical and Population-Based Studies

Open access
Rübsamen, Nicole, Willemse, Eline A. J., Leppert, David, Wiendl, Heinz, Nauck, Matthias, Karch, André, Kuhle, Jens, Berger, Klaus·2022·Frontiers in Neurology
DOI 10.3389/fneur.2022.894119PMC PMC9237479
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Abstract

Introduction: Neurofilament light (NfL) can be detected in blood of healthy individuals and at elevated levels in those with different neurological diseases. We investigated if the choice of biological matrix can affect results when using NfL as biomarker in epidemiological studies. Method: We obtained paired serum and EDTA-plasma samples of 299 individuals aged 37–67 years (BiDirect study) and serum samples of 373 individuals aged 65–83 years (MEMO study). In BiDirect, Passing–Bablok analyses were performed to assess proportional and systematic differences between biological matrices. Associations between serum or EDTA-plasma NfL and renal function (serum creatinine, serum cystatin C, glomerular filtration rate, and kidney disease) were investigated using linear or logistic regression, respectively. All regression coefficients were estimated (1) per one ng/L increase and (2) per one standard deviation increase (standardization using z-scores). In MEMO, regression coefficients were estimated (1) per one ng/L increase of serum or calculated EDTA-plasma NfL and (2) per one standard deviation increase providing a comparison to the results from BiDirect. Results: We found proportional and systematic differences between paired NfL measurements in BiDirect, i.e., serum NfL [ng/L] = −0.33 [ng/L] + 1.11 × EDTA-plasma NfL [ng/L]. Linear regression coefficients for the associations between NfL and renal function did not vary between the different NfL measurements. In MEMO, one standard deviation increase in serum NfL was associated with greater changes in the outcomes than in BiDirect. Conclusion: Although there are differences between serum and EDTA-plasma NfL, results can be used interchangeably if standardized values are used.

AI snapshot

Written from the paper’s full text.

TL;DR

Serum and EDTA-plasma neurofilament light (NfL) show proportional and systematic differences, but regression results using NfL as an independent variable were similar across matrices when standardized values were used. The authors conclude serum and EDTA-plasma NfL can be used interchangeably if effect estimates are based on standardized values.

Key findings

  • In 299 paired BiDirect samples, serum NfL and EDTA-plasma NfL showed proportional and systematic differences: after excluding one outlier, serum NfL [ng/L] = −0.33 [−0.56, −0.06] + 1.11 [1.08, 1.15] × EDTA-plasma NfL [ng/L]. The Bland–Altman mean paired difference was 0.7, with 95.3% of points within the Sfakianakis–Verginis limits.
  • Regression coefficients for associations between NfL and renal function did not vary considerably between serum and EDTA-plasma NfL; for continuous outcomes, absolute differences between serum and EDTA-plasma β per 1 ng/L increase were <0.1% of the outcome ranges, and odds ratios for kidney disease were similar.
  • Standardized (z-score) estimates were comparable across matrices, and mixing serum and EDTA-plasma NfL values produced similar regression coefficients. For example, a one-SD increase in serum NfL was associated with a −0.23 SD change in glomerular filtration rate in BiDirect, with nearly the same result for EDTA-plasma NfL.
  • In MEMO, one SD increase in serum NfL was associated with greater changes than in BiDirect, e.g., 0.44 SD vs. 0.25 SD increase in serum creatinine; calculated EDTA-plasma NfL gave identical standardized coefficients because it was a linear transformation of serum NfL.

Methods

  • Two cohorts were analyzed: BiDirect included 299 paired serum and EDTA-plasma samples from individuals aged 37–67 years (149 women, 150 men); MEMO included 373 serum samples from individuals aged 65–83 years (173 women, 200 men). NfL was measured with the Simoa NF-Light Advantage kit on an HD-X analyser in 1:4 dilution, in duplicate, with intra- and inter-assay coefficients of variation <15%.
  • Passing–Bablok regression and Bland–Altman analysis with Sfakianakis–Verginis limits were used to compare matrices; the cusum test assessed linearity. Associations between NfL and renal function outcomes (serum creatinine, serum cystatin C, glomerular filtration rate, kidney disease) were estimated with linear or logistic regression adjusted for age, sex, and body mass index, using complete-case analyses.
  • Regression coefficients were estimated per 1 ng/L increase and per 1 SD increase using z-score standardization. In MEMO, the BiDirect-derived Passing–Bablok formula was used to calculate EDTA-plasma NfL from serum NfL, and the same regression approach was applied.

Limitations

  • Stated: renal function was not measured at the BiDirect first follow-up examination, when paired serum and EDTA-plasma samples were available, so baseline renal function was used as the outcome solely for illustrative purposes; the authors state they did not aim to predict renal function or establish causality.
  • Stated: MEMO had only serum NfL, so calculated EDTA-plasma NfL was a linear transformation of serum NfL; standardized regression coefficients were therefore identical, and MEMO could not independently validate matrix agreement.
  • Evident: the analyses rely on two German cohorts and use renal-function markers as illustrative outcomes, so generalizability to other populations, outcomes, or NfL assays/platforms is not established by this paper.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.3389/fneur.2022.894119

Cites

34 of 34 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

33 of 41 cited sources checked · 18 supported · 3 flagged · accuracy not yet measured

  • Premisecitation

    Four studies consistently reported higher NfL levels in serum than in plasma.

    “They consistently reported higher NfL levels in serum than in plasma.”
    Quote in the paperSubstantial claim3 of 4 sources checked
    • cites [15] O'Connell, 2019, Neuro biomarker levels measured with high-sensitivity digital ELISA differ between serum and plasma, Bioanalysis. source

      The Results report no statistically significant difference in NfL between paired serum and plasma specimens; in the unpaired analysis, mean NfL was 19.1% lower in serum, also not statistically significant. The Discussion describes NfL levels as comparable between the two blood products, contrary to a consistently higher serum level. This paper reports its own analyses, not findings from four studies. (LLM, conf=0.90)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured
    • cites [16] Hviid, 2020, Reference interval and preanalytical properties of serum neurofilament light chain in Scandinavian adults, Scand J Clin Lab Invest. source
    • cites [17] Sejbaek, 2019, Dimethyl fumarate decreases neurofilament light chain in CSF and blood of treatment naïve relapsing MS patients, J Neurol Neurosurg Psychiatry. source

      The Results section (‘NFL levels correlate in body fluids and are the lowest in plasma’) reports that plasma NfL averaged 76.9% of serum NfL in paired samples; the Discussion describes plasma values as 23% lower. This supports the serum-versus-plasma finding for this study, but this paper alone does not establish that four studies consistently reported it. (LLM, conf=0.86)

      Experimental — accuracy not yet measured
    • cites [18] Altmann, 2021, Seven day pre-analytical stability of serum and plasma neurofilament light chain, Sci Rep. source
  • Premisecitation

    Systematic reviews and meta-analyses encountered limitations when combining results from studies using serum and plasma NfL concentrations.

    “Studies using serum as well as plasma NfL concentrations are abundant in the literature, but systematic reviews and meta-analyses encountered limitations when combining results from these studies (7–9).”
    Quote in the paperSubstantial claim2 of 3 sources checked
    • cites [7] Alirezaei, 2020, Neurofilament light chain as a biomarker, and correlation with magnetic resonance imaging in diagnosis of CNS-related disorders, Mol Neurobiol. source

      The Abstract says many studies have measured NfL in serum or plasma. The “Assays to detect soluble neurofilaments” section says validation studies and meta-analyses emphasized a need to standardize assays, but it does not say that reviews had difficulty combining serum-based and plasma-based results specifically. (LLM, conf=0.79)

      Experimental — accuracy not yet measured
    • cites [8] Gao, 2020, Neurofilament light chain level in traumatic brain injury: a system review and meta-analysis, Medicine. source

      The Results (Meta-analysis; page not provided) pool NfL findings and report substantial heterogeneity, including in the serum and plasma subgroups. The Discussion (page not provided) acknowledges limitations of the meta-analysis, but does not say that combining serum and plasma studies caused those limitations. (LLM, conf=0.82)

      Experimental — accuracy not yet measured
    • cites [9] Zhao, 2019, Neurofilament light chain protein in neurodegenerative dementia: a systematic review and network meta-analysis, Neurosci Biobehav Rev. source
  • Findingcitation

    We confirm the numerical differences between serum and EDTA-plasma NfL levels that have been found in other studies.

    “We confirm the numerical differences between serum and EDTA-plasma NfL levels that have been found in other studies (15–18).”
    Quote in the paperNot a substantial claim3 of 4 sources checked
    • cites [15] O'Connell, 2019, Neuro biomarker levels measured with high-sensitivity digital ELISA differ between serum and plasma, Bioanalysis. source
    • cites [16] Hviid, 2020, Reference interval and preanalytical properties of serum neurofilament light chain in Scandinavian adults, Scand J Clin Lab Invest. source
    • cites [17] Sejbaek, 2019, Dimethyl fumarate decreases neurofilament light chain in CSF and blood of treatment naïve relapsing MS patients, J Neurol Neurosurg Psychiatry. source

      The Results section reports that plasma NfL levels averaged 76.9% of paired serum levels, and the Discussion describes a significant difference. The Methods section does not identify the plasma as EDTA-plasma, so the source supports the numerical serum–plasma difference but not that specific sample type. (LLM, conf=0.84)

      Experimental — accuracy not yet measured
    • cites [18] Altmann, 2021, Seven day pre-analytical stability of serum and plasma neurofilament light chain, Sci Rep. source
  • Premisecitation

    Reference values for serum NfL have already been reported.

    “We decided to present formulas to calculate serum NfL from EDTA-plasma NfL because reference values for serum NfL have already been reported (29).”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [29] Khalil, 2020, Serum neurofilament light levels in normal aging and their association with morphologic brain changes, Nat Commun. source
  • Premisecitation

    Regression coefficients based on categorized independent variables are not comparable across studies.

    “However, regression coefficients based on categorized independent variables are not comparable across studies.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [36] Kahan, 2016, A comparison of methods to adjust for continuous covariates in the analysis of randomised trials, BMC Med Res Methodol. source

      The Methods section defines coefficients for BMI categories relative to an underweight reference group, and the Results discuss power and treatment-effect estimates. Neither addresses whether coefficients based on categorized independent variables are comparable across studies; searches for that claim and for differing category cut-points found no supporting passage. The supplied copy gives no page numbers. (LLM, conf=0.72)

      Experimental — accuracy not yet measured
  • Classified as probably not a substantial claim. 24
  • May combine two claims. 13

  • Classified as probably not a substantial claim.

    Premisecitation

    In those four studies, strengths of correlation were tested via Spearman's correlation coefficient.

    “In all studies, however, strengths of correlation were tested via Spearman's correlation coefficient.”
    Quote in the paperSubstantial claim3 of 4 sources checked
    • cites [15] O'Connell, 2019, Neuro biomarker levels measured with high-sensitivity digital ELISA differ between serum and plasma, Bioanalysis. source
    • cites [16] Hviid, 2020, Reference interval and preanalytical properties of serum neurofilament light chain in Scandinavian adults, Scand J Clin Lab Invest. source
    • cites [17] Sejbaek, 2019, Dimethyl fumarate decreases neurofilament light chain in CSF and blood of treatment naïve relapsing MS patients, J Neurol Neurosurg Psychiatry. source
    • cites [18] Altmann, 2021, Seven day pre-analytical stability of serum and plasma neurofilament light chain, Sci Rep. source

      The Methods (Statistical analyses; page unavailable) say the paper calculated intraclass correlation coefficients (ICCs), not Spearman’s correlation coefficients. The Results (Inter-assay variability; page unavailable) likewise report ICCs for serum and plasma samples. (LLM, conf=0.87)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisereasoning

    Combining patients from multiple cohorts with different sample types (serum or plasma) led to stratification per cohort and a reduction of statistical power.

    “Due to differences in sample type (serum or plasma), results were stratified per cohort, which lead to a reduction of statistical power, while ideally one would convert concentrations between serum and plasma and use them combined.”
    Quote in the paperSubstantial claim4 of 4 sources checked
    • cites [10] Hansson, 2017, Blood-based NfL: a biomarker for differential diagnosis of parkinsonian disorder, Neurology. source

      The Discussion reports that NfL concentrations differed across three cohorts, possibly because of assay variation or plasma-versus-serum effects; the Results report cohort-specific analyses (pages unavailable in our copy). The paper does not say that sample-type differences caused the separate analyses or reduced statistical power, nor does it recommend converting concentrations to combine the cohorts. (LLM, conf=0.86)

      Experimental — accuracy not yet measured
    • cites [11] Akamine, 2020, Renal function is associated with blood neurofilament light chain level in older adults, Sci Rep. source

      The Results table identifies serum NfL in the HC group and plasma NfL in the DM group, and the Discussion reports correlations separately for each group. The Discussion also says the HC analysis was underpowered, but attributes this to its sample size and narrow age distribution—not to stratification by sample type. The paper does not propose converting serum and plasma concentrations to combine the groups. (LLM, conf=0.88)

      Experimental — accuracy not yet measured
    • cites [12] Lombardi, 2019, Muscle and not neuronal biomarkers correlate with severity in spinal and bulbar muscular atrophy, Neurology. source

      The Methods section on NfL, CK, and creatinine measurements identifies plasma for the UK cohort and serum for the Italian cohort; the Results report cohort-specific analyses. Our copy does not say that sample-type differences caused the analyses to be separated or that separating them reduced statistical power. No page numbers are available in our copy. (LLM, conf=0.83)

      Experimental — accuracy not yet measured
    • cites [13] Lu, 2015, Neurofilament light chain: a prognostic biomarker in amyotrophic lateral sclerosis, Neurology. source

      The Methods (Statistical analysis; page unavailable) say the authors used cohort-specific tertile cutoffs because serum and plasma NfL were different measures, but explicitly analyzed the two cohorts together. The Results (Survival analyses; page unavailable) say combining cohorts increased the number of patients; the paper does not report the claimed reduction in statistical power. (LLM, conf=0.88)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    Passing-Bablok regression analyses allow estimating proportional and systematic differences between two measurements and calculating parameters that allow for correction.

    “Passing–Bablok regression analyses, in contrast to correlation coefficients and Bland–Altman plots, allow to estimate proportional and systematic differences between two measurements and to calculate parameters that allow for correction (19).”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [19] Bilić-Zulle, 2011, Comparison of methods: passing and Bablok regression, Biochem Medica. source

      The Conclusion (page not provided) says Passing–Bablok regression estimates constant and proportional bias and calculates parameters that allow correction. The Data analyses section says correlation coefficients cannot detect those differences, but it only lists Bland–Altman plots as another method; it does not support the claimed contrast with those plots. (LLM, conf=0.85)

      Experimental — accuracy not yet measured

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The Bland-Altman plot is a simple way to evaluate any bias between the mean differences.

    “The Bland–Altman plot is a simple way to evaluate any bias between the mean differences (27).”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [27] Giavarina, 2015, Understanding Bland Altman analysis, Biochem Medica. source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductcitation

    The relevant quality criteria were considered for the creatinine and cystatin C assays.

    “The relevant quality criteria were considered (24).”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [24] 2015, LaboratoriumsMedizin source

      Table B1a gives permissible deviations and applicable concentration intervals for creatinine in plasma, serum, or whole blood; Table B1b gives corresponding criteria for urine creatinine. The passages do not identify cystatin C-specific criteria, and this guideline cannot establish whether the citing authors actually considered the criteria in their assays. (LLM, conf=0.82)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    Correlation describes a linear relationship between two sets of data but not their agreement; it does not quantify the proportional or systematic difference between two methods, so it does not allow deriving a formula for conversion between sampling methods.

    “Correlation describes linear relationship between two sets of data, but not their agreement; it does not quantify the proportional or systematic difference between two methods (19), so it does not allow to derive a formula for conversion between sampling methods.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [19] Bilić-Zulle, 2011, Comparison of methods: passing and Bablok regression, Biochem Medica. source

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    NfL is a structural protein that can be detected in the blood at elevated levels in a variety of neurological diseases.

    “NfL is a structural protein that can be detected in the blood at elevated levels in a variety of neurological diseases (2–5).”
    Quote in the paperNot a substantial claim3 of 4 sources checked
    • cites [2] Thebault, 2020, Blood neurofilament light chain: the neurologist's troponin?, Biomedicines. source
    • cites [3] Khalil, 2018, Neurofilaments as biomarkers in neurological disorders, Nat Rev Neurol. source
    • cites [4] Bridel, 2019, Diagnostic value of cerebrospinal fluid neurofilament light protein in neurology, JAMA Neurol. source
    • cites [5] Gisslén, 2016, Plasma concentration of the neurofilament light protein (NFL) is a biomarker of CNS injury in HIV infection: a cross-sectional study, EBioMedicine. source

      The Discussion describes NFL’s structural role in axons, and the Results report elevated plasma NFL in some groups with HIV-related CNS injury. The Discussion says elevations across several other neurological diseases have been shown in CSF; it presents plasma NFL’s usefulness in those settings as an extrapolation, not an established finding. (LLM, conf=0.87)

      Experimental — accuracy not yet measured

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductcitation

    Regression models were adjusted for age, sex, and body mass index.

    “adjusted for age, sex, and body mass index (31)”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [31] Manouchehrinia, 2020, Confounding effect of blood volume and body mass index on blood neurofilament light chain levels, Ann Clin Transl Neurol. source

      The Materials and Methods passage says the multiple linear regression models were adjusted for sex and age at sampling, with BMI assessed as a predictor. It separately describes analyses controlling for BMI, but does not establish that those regression models were adjusted for age, sex, and BMI together. (LLM, conf=0.86)

      Experimental — accuracy not yet measured

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductcitation

    NfL was entered as a linear predictor term after confirming linearity of the associations with fractional polynomial analyses.

    “NfL was entered as a linear predictor term after confirming linearity of the associations with fractional polynomial analyses (32).”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [32] Royston, 1999, The use of fractional polynomials to model continuous risk variables in epidemiology, Int J Epidemiol. source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Lu et al. combined serum and plasma NfL by using cohort-specific tertile cut-off levels in Cox regression analysis of survival.

    “Lu et al. (13) combined serum and plasma NfL by using cohort-specific tertile cut-off levels in Cox regression analysis of survival.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [13] Lu, 2015, Neurofilament light chain: a prognostic biomarker in amyotrophic lateral sclerosis, Neurology. source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    Associations between serum NfL and renal function were investigated using linear or logistic regression models adjusted for age, sex, and body mass index.

    “Associations between serum NfL and renal function (serum creatinine, glomerular filtration rate estimated via the CKD-EPI equation (30), and glomerular filtration rate ≤ 60 mL/min/1.73 m2 as indicator of kidney disease) were investigated using linear or logistic regression models [adjusted for age, sex, and body mass index (31)], respectively.”
    Quote in the paperNot a substantial claim2 of 2 sources checked
    • cites [30] Inker, 2012, Estimating glomerular filtration rate from serum creatinine and cystatin C, N Engl J Med. source
    • cites [31] Manouchehrinia, 2020, Confounding effect of blood volume and body mass index on blood neurofilament light chain levels, Ann Clin Transl Neurol. source

  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation

    Akamine et al. reported a relationship between blood NfL concentration and renal function in healthy individuals (serum NfL) and patients with diabetes mellitus (plasma NfL).

    “Akamine et al. (11) have already reported on the relationship between blood NfL concentration and renal function in healthy individuals (based on serum NfL) and patients with diabetes mellitus (based on plasma NfL).”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [11] Akamine, 2020, Renal function is associated with blood neurofilament light chain level in older adults, Sci Rep. source

  • May combine two claims.

    Findingown data

    An increase of serum NfL by one SD was associated with a decrease of 0.23 SD in glomerular filtration rate; results for EDTA-plasma NfL were nearly the same.

    “For example, an increase of serum NfL by one SD was associated with a decrease of 0.23 SD in glomerular filtration rate; results for EDTA-plasma NfL were nearly the same.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The regression models adjusted for age, sex, and body mass index adequately control for confounding in the associations between NfL and renal function.

  • May combine two claims.

    Findingreasoning

    Standardizing outcomes and independent variables using z-scores resulted in identical regression coefficients because calculated EDTA-plasma NfL was just a linear transformation of serum NfL.

    “Standardizing outcomes and independent variables using z-scores resulted in identical regression coefficients because calculated EDTA-plasma NfL was just a linear transformation of serum NfL.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The Passing–Bablok conversion formula derived in BiDirect is valid for calculating EDTA-plasma NfL from serum NfL in MEMO.
    • Rests on an assumption: The regression models adjusted for age, sex, and body mass index adequately control for confounding in the associations between NfL and renal function.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingown data

    We confirm the positive association between NfL (as dependent variable) and creatinine (as predictor) in our cohorts.

    “We are aware of this finding and can confirm the positive association between NfL (as dependent variable) and creatinine (as predictor) in our cohorts (data not shown).”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The regression models adjusted for age, sex, and body mass index adequately control for confounding in the associations between NfL and renal function.

  • May combine two claims.

    Findingown data

    Regression coefficients from the two cohorts can be compared, revealing greater effect sizes among elderly individuals (MEMO) compared to 37-67-year-old individuals.

    “At one glance, these regression coefficients can be compared to each other, revealing greater effect sizes among elderly individuals (MEMO) compared to 37–67-year-old individuals.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The regression models adjusted for age, sex, and body mass index adequately control for confounding in the associations between NfL and renal function.
    • Rests on an assumption: The greater effect sizes in MEMO compared to BiDirect are due to the older age of the MEMO cohort.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    Processing was done according to the standard operating procedures in BiDirect and MEMO.

    “Processing was done according to the standard operating procedures in BiDirect and MEMO.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationown data

    Although there are differences between serum and EDTA-plasma NfL, results can be used interchangeably if standardized values are used.

    “Although there are differences between serum and EDTA-plasma NfL, results can be used interchangeably if standardized values are used.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Premisecitation

    Differences between serum and plasma are known for other biomarkers, due to release of intracellular substances caused by sample clotting.

    “Differences between serum and plasma are known for other biomarkers, according to the release of intracellular substances caused by sample clotting (14).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [14] Boeynaems, 2004, Evaluation of a new generation of plastic evacuated blood-collection tubes in clinical chemistry, therapeutic drug monitoring, hormone and trace metal analysis, Clin Chem Lab Med. source

  • May combine two claims.

    Interpretationown data

    There are proportional and systematic differences between NfL assays, but results are similar when using standardized NfL and outcome values.

    “We found proportional and systematic differences between NfL assays, but we show that results were similar when using standardized NfL and outcome values.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The regression models adjusted for age, sex, and body mass index adequately control for confounding in the associations between NfL and renal function.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductnone given

    Samples were run in duplicate by board-certified technicians blinded to clinical information.

    “Samples were run in duplicate by board-certified technicians blinded to clinical information.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductown data

    Continuous outcome variables were approximately normally distributed so they were not transformed before applying the linear regression analyses.

    “Continuous outcome variables were approximately normally distributed so they were not transformed before applying the linear regression analyses.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    In case of missing outcome or independent variable values, complete-case analyses were performed.

    “In case of missing outcome or independent variable values, we performed complete-case analyses.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The analytical sensitivity of quantifying NfL in blood is greatly increased by Simoa technology compared to classical ELISA and ECL technologies.

    “The analytical sensitivity quantifying NfL in blood has been greatly increased by utilizing the single-molecule assay (Simoa) technology, as compared to the classical ELISA and ECL technologies (6), facilitating studies into NfL as biomarker for a wide range of clinical conditions on a large scale.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [6] Kuhle, 2016, Comparison of three analytical platforms for quantification of the neurofilament light chain in blood samples: ELISA, electrochemiluminescence immunoassay and Simoa, Clin Chem Lab Med. source

  • Classified as probably not a substantial claim.

    Study design and conductreasoning

    In BiDirect, paired serum and EDTA-plasma samples were consecutively included in the same run to avoid inter- or intraplate variation influencing the results of the pairwise comparison.

    “In BiDirect, paired serum, and EDTA-plasma samples were consecutively included in the same run to avoid any inter- or intraplate variation influencing the results of the pairwise comparison.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    Samples have never been thawed prior to NfL analyses.

    “Samples have never been thawed prior to NfL analyses.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    In BiDirect, 300 paired serum and EDTA-plasma samples were selected to represent a uniform distribution of age and sex.

    “Three hundred paired serum and EDTA-plasma samples from the first follow-up examination (2013–2015) were selected in a way to represent a uniform distribution of age and sex in BiDirect.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductown data

    Renal function was not measured at the first follow-up examination in BiDirect, so renal function at baseline was used as outcome solely for illustrative purposes.

    “It has to be kept in mind that renal function was not measured at the first follow-up examination in BiDirect (for which paired sera and EDTA-plasma samples were available), so we used renal function at baseline as outcome solely for illustrative purposes.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    The research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

    “The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    The studies involving human participants were reviewed and approved by the Joint Ethics Committee of the University of Münster and the Westphalian Chamber of Physicians.

    “The studies involving human participants were reviewed and approved by Joint Ethics Committee of the University of Münster and the Westphalian Chamber of Physicians.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    The patients/participants provided their written informed consent to participate in this study.

    “The patients/participants provided their written informed consent to participate in this study.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Interpretationreasoning

    The derived conversion formula offers one way to compare results among several studies.

    “This offers one way to compare results among several studies.”
    Quote in the paperSubstantial claim
32 of 32

  • The authors state this as an assumption.

    Passing–Bablok regression assumes that measurement errors in both measurements have the same distribution, which not necessarily has to be normal.

    “Passing–Bablok regression analyses assume that measurement errors in both measurements have the same distribution, which not necessarily has to be normal, so we did not log-transform NfL values in these analyses (26).”

  • The authors state this as an assumption.

    Passing–Bablok regression assumes a linear relationship between two measurements.

    “As Passing–Bablok regression assumes a linear relationship between two measurements, the cumulative sum linearity test (cusum test) was used to investigate if residuals were randomly distributed above and below the regression line.”

  • The paper relies on this without support.

    NfL has the same biological effect across studies.

    “although NfL would have the same biological effect across studies.”

  • The paper relies on this without support.

    The Passing–Bablok conversion formula derived in BiDirect is valid for calculating EDTA-plasma NfL from serum NfL in MEMO.

    “In MEMO, we used the Passing–Bablok formula that was derived in BiDirect to calculate EDTA-plasma NfL values from serum NfL”

  • The paper relies on this without support.

    The regression models adjusted for age, sex, and body mass index adequately control for confounding in the associations between NfL and renal function.

    “adjusted for age, sex, and body mass index”

  • The paper relies on this without support.

    The higher serum NfL values in MEMO compared to BiDirect are due to the different age ranges.

    “Serum NfL values were higher in MEMO than in BiDirect because of the different age ranges”

  • The paper relies on this without support.

    The greater effect sizes in MEMO compared to BiDirect are due to the older age of the MEMO cohort.

    “revealing greater effect sizes among elderly individuals (MEMO) compared to 37–67-year-old individuals”
7 of 7

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Cystatin C range has inconsistent units

    Minor

    Table 2 labels the serum cystatin C range in mg/dL, while Table 1 reports cystatin C in mg/L. The numerical range of 2.25 comes from Table 1's maximum minus minimum (2.82 − 0.57), so its unit should be mg/L.

1 of 1

Cites

Flagged first, then by citations

Research works printed but not linked: 2

  1. Gujarati, 2003, Regression on standardized variables, 173
  2. Gujarati, 2003, Scaling and units of measurement, 169

Cited by

Sorted by citations

Related

Authors
Rübsamen, N., Willemse, E. A. J., Leppert, D., Wiendl, H., Nauck, M., Karch, A., Kuhle, J., & Berger, K.
Affiliations
  • University of Münster (DE)
  • University of Basel (CH)
  • Universitätsmedizin Greifswald (DE)
Corresponding author
Rübsamen, Nicole
ORCID
Venue
Frontiers in Neurology
Publisher
Frontiers Media SA
Published
2022-06-14
Volume
13
Pages
894119-894119
ISSN
1664-2295 (ISSN-L)
DOI
10.3389/fneur.2022.894119
PMC
PMC9237479
OpenAlex
W4282841511
Semantic Scholar
5519de6f4d67e1fc5e646f2f29bb95a5fe6bd6a9
Cited by
27
References
34
Citations by year
2026: 11 · 2025: 7 · 2024: 5 · 2023: 3 · 2022: 1
FWCI
2.05
Type
journal article
Language
en
Open access
Licence
Locations
  • Frontiers in Neurology (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Pure Amsterdam UMC (publishedVersion, cc-by)
  • PubMed Central (submittedVersion, cc-by)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion)
  • Amsterdam UMC (VU Amsterdam) - Institutional Repository (submittedVersion, other-oa)
  • Data Archiving and Networked Services (DANS) (submittedVersion, other-oa)
Funders
  • Deutsche Forschungsgemeinschaft
  • Bundesministerium für Bildung und Forschung
  • Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung
Topics
  • Health Sciences › Medicine › Physiology › Clinical Laboratory Practices and Quality Control
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Skin and Cellular Biology Research
  • Health Sciences › Medicine › Pathology and Forensic Medicine › Multiple Sclerosis Research Studies
Keywords
neurofilament light chain, serum, EDTA plasma, standardization, renal function, cystatin C, glomerular filtration rate, kidney disease, neurodegeneration biomarkers, population-based study

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-17.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-17.

Cited sources are checked by gpt-6-sol.

Statistics and arithmetic are recomputed, not judged.

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