# NfL (Neurofilament light chain)

Neurofilament light chain (NfL) is a structural protein from inside large, myelinated nerve fibers. When nerve axons are injured, NfL leaks into the spinal fluid and blood. Ultra-sensitive assays (like Simoa, from Quanterix) can now measure it at tiny picogram-per-milliliter levels in blood. That turned it into a disease-agnostic marker of axon damage. NfL rises with age and across many conditions: multiple sclerosis, ALS, Alzheimer's, frontotemporal dementia, traumatic brain injury, and stroke. In MS, it tracks relapses and treatment response. In ALS, it tracks progression and survival. In Alzheimer's, it indexes neurodegeneration within the 'ATN(N)' framework. It does not tell you the cause, and you must read it against age-adjusted reference values. But change over time within one person carries real prognostic weight.

## Sources

- Khalil M, Teunissen CE, Otto M, Piehl F, Sormani MP, Gattringer T, et al.. (2018). Neurofilaments as biomarkers in neurological disorders. Nature Reviews Neurology. https://doi.org/10.1038/s41582-018-0058-z
- Khalil M, Teunissen CE, Lehmann S, Otto M, Piehl F, Ziemssen T, et al.. (2024). Neurofilaments as biomarkers in neurological disorders - towards clinical application. Nature Reviews Neurology. https://doi.org/10.1038/s41582-024-00955-x
- Kuhle J, Kropshofer H, Haering DA, Kundu U, Meinert R, Barro C, et al.. (2019). Blood neurofilament light chain as a biomarker of MS disease activity and treatment response. Neurology. https://doi.org/10.1212/WNL.0000000000007032

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_Canonical: https://longevity-switzerland.com/en/glossary/nfl-neurofilament-light · Part of Longevity Cities · Updated 2026-06-22_