NfL was measured in CSF and serum using the Simoa Nf-light kit and provided consumables in the Simoa SR-X Analyzer (Quanterix, Lexington, MA, USA).26 (link) The NfL assay was performed according to the manufacturer's instructions and protocol, as previously described.27 All samples were measured under blinded conditions at the Medical University of Vienna, Department of Neurology.
As sNfL concentrations increase with age and decrease with BMI under physiological conditions, we calculated age- and BMI-adjusted Z scores. This allows to quantify the deviation of each patient's individual sNfL value in comparison to control persons of the same age and BMI, based on a recently published reference database.19 (link) Z score >1.5 was defined as elevated (termed as ‘positive’), Z score ≤1.5 was defined as ‘negative’. A Z score >3 was considered as ‘high’, a Z score >1.5 and ≤3 was considered as ‘moderately elevated’.
As sNfL concentrations increase with age and decrease with BMI under physiological conditions, we calculated age- and BMI-adjusted Z scores. This allows to quantify the deviation of each patient's individual sNfL value in comparison to control persons of the same age and BMI, based on a recently published reference database.19 (link) Z score >1.5 was defined as elevated (termed as ‘positive’), Z score ≤1.5 was defined as ‘negative’. A Z score >3 was considered as ‘high’, a Z score >1.5 and ≤3 was considered as ‘moderately elevated’.
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