OBJECTIVE: This exploratory study investigates if neurofilament light chain (NfL) is excreted in the urine and whether this depends on plasma NfL (pNfL) levels and kidney function in terms of eGFR and urine albumin-creatinine ratio (uACR). METHODS: Using a computer algorithm, we identified excess urine and plasma from routine testing of uACR and eGFR in patients 45-50 years old. Up to 17 paired urine-plasma samples in each of six categories of kidney function defined by uACR and eGFR were analysed for NfL, and the urinary NfL-creatinine ratio (uNCR) was calculated to correct for urine dilution. RESULTS: In the 35 subjects with normal eGFR (>
90 ml/min/1.73 m CONCLUSIONS: Our results show that the urinary NfL excretion in subjects with normal kidney function and normal pNfL levels is very low. Thus, the increased pNfL often observed in patients with low eGFR seems not to be explained by impaired urinary NfL excretion, and urine is generally not a suitable matrix for NfL measurements.