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Blood Test Tracker

Neurofilament Light Chain (NfL)

A protein released when nerve cells are injured. Levels rise with age, so labs use age-based ranges, and a high result does not point to one cause.

AI-verified against cited sources. Awaiting expert reviewAlso called NfL, NF-L, sNfLLOINC 101281-4

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What it is

Neurofilament light chain (NfL) is a protein that helps give nerve fibers their structure. When nerve cells are injured, some NfL leaks out into the spinal fluid and then into the blood. This blood test measures it in plasma or serum. It does not show where the injury is or what caused it. NfL goes up with age, so labs compare your result with people your age.

Why it matters

NfL is a general marker of nerve cell injury. Clinicians look at it along with symptoms, an exam and imaging when they are assessing conditions such as multiple sclerosis, ALS, nerve damage and dementia. A result in the usual range for your age does not rule out a nerve condition, and a high result does not point to one cause. Age, kidney function and body size also move the number, so it needs careful reading in context.

If it’s high

A high NfL means there is more of this protein in your blood than is usual for your age. That is a general sign of nerve cell injury or turnover, and it does not say what caused it. Several everyday factors, such as reduced kidney function and lower body weight, can also push it up.

Common causes

  • Natural rise with age (labs use age-based ranges for this reason)
  • Reduced kidney function
  • Lower body weight or smaller blood volume
  • Heart and blood vessel risk factors, which are linked with NfL levels in studies
  • A recent head injury, stroke or other injury to the brain or spinal cord
  • Nerve damage outside the brain and spinal cord (peripheral neuropathy)
  • Conditions that injure nerve cells, such as multiple sclerosis, ALS, frontotemporal dementia, Alzheimer's disease or atypical parkinsonian disorders

What can help

  • Ask your clinician to read NfL together with your age, kidney function, symptoms and exam
  • Ask whether repeating the test at the same lab and with the same method would be useful
  • Tell your clinician about any recent head injury, new weakness, numbness or changes in walking, vision or thinking

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on age. Choose an age to see the one that applies.

Children and teens 5 ranges

See NfL by age and sex, with the U.S. survey numbers where they exist.

What can affect your result

  • Age: levels rise steadily across adulthood, faster after about 50
  • Body mass index and blood volume: higher body size is linked to lower levels
  • Kidney function: reduced function is linked to higher levels
  • Assay method and sample type (serum or plasma)
  • Recent injury or stroke, and conditions that injure nerve cells or nerves
  • Biotin: ARUP asks patients to stop biotin supplements (vitamin B7) for 72 hours before collection for its NfL tests, which use an electrochemiluminescence immunoassay.
  • Age: levels rise steadily with age, faster after about 50, so results are read against an age-based range.
  • Body size: a higher body mass index (more blood volume) is linked to lower levels, and the effect is clearest in middle age.
  • Kidney function: reduced kidney function is linked to higher levels, especially after about 60.
  • Method and sample type: assays read on very different scales, and serum and plasma values are not identical. Compare results only from the same lab, method and sample type.
  • Recent injury to the brain, spinal cord or nerves (such as a head injury or stroke) can raise levels for some time.

When to talk to a clinician

NfL on its own is not an emergency. See a clinician soon for new weakness, numbness, vision changes, trouble walking or speaking, or new confusion, or after a head injury. Call 911 or your local emergency number for sudden face drooping, arm weakness, trouble speaking or severe confusion.

Questions you could ask

  • What is NfL being used for in my situation?
  • Should we repeat it, and if so, at the same lab?
  • Is my result above the range for my age and for this method?
  • Could my kidney function, body weight or a recent injury explain it?
  • What follow-up, if any, would you suggest given my symptoms?

Questions people ask

Does a high NfL mean I have a brain or nerve disease?

Not by itself. NfL rises with age, reduced kidney function and many conditions. It shows that nerve cells may be under strain, but not why. Your clinician reads it with your symptoms, exam and other tests.

Why does my lab's range depend on my age?

NfL climbs steadily as people get older, and faster after about 50. For example, Mayo Clinic Laboratories lists an upper limit of 22.4 pg/mL for ages 50 to 54 and 37.1 pg/mL for ages 70 to 74. Other labs and methods use different numbers.

Can I compare NfL results from two different labs?

Usually not. In one study, one common method read about 85% lower than another on the same blood samples. Compare results only when they come from the same lab, method and sample type.

Show the science and sources

For clinicians and researchers

Neurofilament light chain is a subunit of the neuronal intermediate filament cytoskeleton that is released into CSF and then blood after axonal damage (Khalil 2024). Plasma and CSF values correlate closely, with CSF about 55-fold higher (Booth 2025). Blood levels rise roughly exponentially with age, more steeply after about 50, and fall with higher BMI (Benkert 2022); renal function gains importance after about 60 (Koini 2021), and in 70-year-olds the median plasma NfL was 18.8 pg/mL with chronic kidney disease versus 14.1 without (Dittrich 2023). Assays are not interchangeable. In a comparison that included 718 people with MS, serum Elecsys values were highly correlated with Simoa (r = 0.991) but averaged 85% lower, so each platform needs its own reference limits (Booth 2025). Mayo's plasma limits above come from a chemiluminescent enzyme immunoassay; ARUP's ECLIA-based tests print the interval on the report, and its serum test also offers a Z score. In Mayo's earlier Simoa-based study of 1,100 cognitively unimpaired adults aged 20 to 95, NfL rose about 3% per year of age and sex had no significant effect, the same age pattern but a different numeric scale from the clinical assay above (Mayo 2022). Age- and BMI-adjusted Z scores from Simoa reference data outperformed raw cutoffs for predicting disease activity in MS; a Z score above 1.5 was linked to higher odds of future activity (Benkert 2022). The highest blood NfL levels occur in ALS, frontotemporal dementia, atypical parkinsonian disorders, MS and HIV-associated neurocognitive disorder, with a more modest rise in Alzheimer's disease (Hansson 2022). Related LOINC codes exist for NfL Z score (111552-6) and molar concentration in plasma (112614-3).

LOINC 101281-4 (primary). Specimen: serum-or-plasma.

Sources

  1. Neurofilament Light Chain, Plasma (Mayo test ID NFLP), Mayo Clinic Laboratories Extended Catalog (testcatalog.org) (2026)
  2. Plasma neurofilament light chain (NfL) reference interval determination in an Age-stratified cognitively unimpaired cohort, Clinica Chimica Acta (2022)
  3. Neurofilament Light Chain, Plasma (ARUP test 3021399), ARUP Laboratories (2026)
  4. Neurofilament Light Chain, Serum (ARUP test 3021400), ARUP Laboratories (2026)
  5. Neurofilaments as biomarkers in neurological disorders - towards clinical application, Nature Reviews Neurology (2024)
  6. Serum neurofilament light chain for individual prognostication of disease activity in people with multiple sclerosis: a retrospective modelling and validation study, The Lancet Neurology (2022)
  7. Validation and generation of age-specific reference intervals for a new blood neurofilament light chain assay, Clinica Chimica Acta (2025)
  8. Factors influencing serum neurofilament light chain levels in normal aging, Aging (Albany NY) (2021)
  9. Association of Chronic Kidney Disease With Plasma NfL and Other Biomarkers of Neurodegeneration: The H70 Birth Cohort Study in Gothenburg, Neurology (2023)
  10. The multifaceted role of neurofilament light chain protein in non-primary neurological diseases, Brain (2023)
  11. Plasma neurofilament light chain concentration in the inherited peripheral neuropathies, Neurology (2018)
  12. The Alzheimer's Association appropriate use recommendations for blood biomarkers in Alzheimer's disease, Alzheimer's & Dementia (2022)
  13. LOINC 101281-4: Neurofilament light chain [Mass/volume] in Serum or Plasma by Immunoassay, LOINC via NLM Clinical Tables

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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